arch: arm: Cortex-A/R: add pre stack platform init

Adds platform (SoC) specific startup hook executed before the stack is
initialised.

Signed-off-by: Tavish Naruka <[email protected]>

Author: Tavish Naruka

arch/arm/core/Kconfig

@@ -174,6 +174,14 @@ config PLATFORM_SPECIFIC_INIT
 
 	  This option is deprecated, use SOC_RESET_HOOK instead.
 
+config PLATFORM_SPECIFIC_PRE_STACK_INIT
+	bool "Platform (SOC) specific startup hook executed before the stack is initialised"
+	help
+	  The platform specific initialization code (z_arm_platform_pre_stack_init) is
+	  executed in the early startup code right after the registers are set to known
+	  values and before stack is set up. Note that this code cannot use the stack unlike
+	  z_arm_platform_init.
+
 config FAULT_DUMP
 	int "Fault dump level"
 	default 2

arch/arm/core/cortex_a_r/reset.S

@@ -209,6 +209,10 @@ EL1_Reset_Handler:
     mcr p15, 1, r0, c9, c1, 0
 #endif
 
+#if defined(z_arm_platform_pre_stack_init)
+    bl z_arm_platform_pre_stack_init
+#endif
+
     ldr r0, =arm_cpu_boot_params
 
 #if CONFIG_MP_MAX_NUM_CPUS > 1