Don't run step on LF OpenBMC

Summary: See T250939868 for context, step is currently not compatible with LF OpenBMC as we don't ensure mountpoints targeted at the SPI flash are unmounted as we do with Meta OpenBMC releases

Test Plan:
Unit tests, run step in a ventura unit, ensure it gets skipped (thanks cjcon90): P2114946883

Deploy flashy to a test morgan800cc device:
```
~/fbcode/openbmc/openbmc/tools/flashy$ scripts/run_flashy_remote.sh  --device mtd:flash0 --imagepath $( (cd $(mktemp -d) && fbpkg fetch openbmc.image.morgan800cc && readlink -f flash-morgan800cc) ) --host fboss329013173-oob.ash7 --dry-run
```

Run step, ensure it runs as expected:
```
root@fboss329013173-oob:~# /run/flashy/checks_and_remediations/common/91_expose_real_flash0_on_secondary_boot_g6 --device mtd:flash0 --ima
gepath /dev/null
2026/01/12 03:02:22 Not starting PetWatchdogLoop; BMC Lite
2026/01/12 03:02:22 Starting: checks_and_remediations/common/91_expose_real_flash0_on_secondary_boot_g6
2026/01/12 03:02:23 WDT2 second boot code flag @ 0x1e620064 not active (current value = 0x0), skipping step
2026/01/12 03:02:23 Finished: checks_and_remediations/common/91_expose_real_flash0_on_secondary_boot_g6
```

Reviewed By: cjcon90

Differential Revision: D90387321

fbshipit-source-id: 96d6de69b95e06bf0eca79d7fedb211433c83a9f

Author: kawmarco

tools/flashy/checks_and_remediations/common/91_expose_real_flash0_on_secondary_boot_g6.go

@@ -50,6 +50,12 @@ func ExposeRealFlash0OnSecondaryBootG6(stepParams step.StepParams) step.StepExit
 		return step.ExitSafeToReboot{Err: errors.Errorf("Unable to fetch machine: %v", err)}
 	}
 
+	// T250939868: LF OpenBMC doesn't support this as the overlay partitions are still mounted
+	if utils.IsLFOpenBMC() {
+		log.Printf("Skipping step for LF OpenBMC")
+		return nil
+	}
+
 	// Bail if not running on AST2600
 	if machine != "armv7l" {
 		log.Printf("Remediation handles only AST2600")

tools/flashy/checks_and_remediations/common/91_expose_real_flash0_on_secondary_boot_g6_test.go

@@ -154,6 +154,33 @@ func TestExposeRealFlash0OnSecondaryBootAstG6(t *testing.T) {
 
 	})
 
+	t.Run("Should skip if LF OpenBMC", func(t *testing.T) {
+		var buf bytes.Buffer
+		log.SetOutput(&buf)
+
+		GetMachineOrig := utils.GetMachine
+		defer func() { utils.GetMachine = GetMachineOrig }()
+		IsLFOpenBMCOrig := utils.IsLFOpenBMC
+		defer func() { utils.IsLFOpenBMC = IsLFOpenBMCOrig }()
+
+		utils.GetMachine = func() (string, error) { return "armv7l", nil }
+		utils.IsLFOpenBMC = func() bool { return true }
+
+		res := ExposeRealFlash0OnSecondaryBootG6(step.StepParams{})
+
+		if res != nil {
+			t.Errorf("Expected ExposeRealFlash0OnSecondaryBoot() to return nil, got %v", res)
+		}
+
+		re_expected_log_buffer := "" +
+			"^[^\n]+Skipping step for LF OpenBMC"
+
+		if !regexp.MustCompile(re_expected_log_buffer).Match(buf.Bytes()) {
+			t.Errorf("Unexpected log buffer: %v", buf.String())
+		}
+
+	})
+
 	t.Run("Should bail out if not running on AST2600", func(t *testing.T) {
 		var buf bytes.Buffer
 		log.SetOutput(&buf)