uart_buffering: Process UART TX explicitly when disabled interrupt

When interrupts are disabled we should follow the same path like in
case when we are in interrupt context. This will fix infinite loop when
calling uart_flush_output() (eg. when ASSERT is triggered) with disabled
interrupts

BUG=b:190597666
BRANCH=none
TEST=Trigger ASSERT when interrupts are disabled. Make sure that panic
     message is shown. Perform this test on following cores:
     cortex-m - this is the most common core, eg. bloonchipper
     minute-ia - this is used for Intel Sensor Hub (cros_ish)
                 eg. drallion board
     riscv-rv32i - hayato (asurada family) has EC chip based on risc-v
     nds32 - ampton (octopus family) has EC chip based on it

Signed-off-by: Patryk Duda <[email protected]>
Change-Id: If88881c6444a40a9c6459d8a6ff42f3ad4c4d750
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2953234
Commit-Queue: Marcin Wojtas <[email protected]>
Tested-by: Patryk Duda <[email protected]>
Reviewed-by: Aseda Aboagye <[email protected]>

Author: duda-patryk

common/uart_buffering.c

@@ -261,7 +261,7 @@ void uart_flush_output(void)
 
 	/* Loop until buffer is empty */
 	while (tx_buf_head != tx_buf_tail) {
-		if (in_interrupt_context()) {
+		if (in_interrupt_context() || !is_interrupt_enabled()) {
 			/*
 			 * Explicitly process UART output, since the UART
 			 * interrupt may not be able to preempt the interrupt