lib: sbi: Introduce an early console buffer for caching early prints

The console device is registered by platform only in early_init()
callback so any prints before this point will be lost. Introduce an
early console buffer for caching prints before platform early_init().

For crashes before platform early_init(), users can simply dump the
contents of the console_early_buffer[] string using a debugger. The
relative address of the console_early_buffer[] string can be found
using following two commands:

CONSOLE_EARLY_FIFO_ADDR=`${CROSS_COMPILE}objdump -D \
build/platform/generic/firmware/fw_dynamic.elf | \
grep "<console_early_fifo>:" | awk '{print $1}'`

${CROSS_COMPILE}objdump -R build/platform/generic/firmware/fw_dynamic.elf | \
grep $CONSOLE_EARLY_FIFO_ADDR | awk '{print $3}'

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-By: Himanshu Chauhan <hchauhan@ventanamicro.com>

lib/sbi/Kconfig

@@ -1,6 +1,10 @@
 # SPDX-License-Identifier: BSD-2-Clause
 
-menu "SBI Extension Support"
+menu "Generic SBI Support"
+
+config CONSOLE_EARLY_BUFFER_SIZE
+	int "Early console buffer size (bytes)"
+	default 256
 
 config SBI_ECALL_TIME
 	bool "Timer extension"