fastboot: Add default fastboot_set_reboot_flag implementation

Default implementation of fastboot_set_reboot_flag function that depends
on "bcb" commands could be used in general case if there are no need to
make any platform-specific implementation, otherwise it could be
disabled via Kconfig option FASTBOOT_USE_BCB_SET_REBOOT_FLAG.

Please note that FASTBOOT_USE_BCB_SET_REBOOT_FLAG is mutually exclusive
with some platforms which already have their own implementation of this
function.

Signed-off-by: Roman Kovalivskyi <roman.kovalivskyi@globallogic.com>
diff --git a/drivers/fastboot/Kconfig b/drivers/fastboot/Kconfig
index d4436df..4352ba6 100644
--- a/drivers/fastboot/Kconfig
+++ b/drivers/fastboot/Kconfig
@@ -165,6 +165,18 @@
 	  relies on the env variable partitions to contain the list of
 	  partitions as required by the gpt command.
 
+config FASTBOOT_USE_BCB_SET_REBOOT_FLAG
+	bool "Use BCB by fastboot to set boot reason"
+	depends on CMD_BCB && !ARCH_MESON && !ARCH_ROCKCHIP && !TARGET_KC1 && \
+	  !TARGET_SNIPER && !TARGET_AM57XX_EVM && !TARGET_DRA7XX_EVM
+	default y
+	help
+	  Fastboot could implement setting of reboot reason in a generic fashion
+	  via BCB commands. BCB commands are able to write reboot reason into
+	  command field of boot control block. In general case it is sufficient
+	  implementation if your platform supports BCB commands and doesn't
+	  require any specific reboot reason handling.
+
 endif # FASTBOOT
 
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