powerpc/mpc8xx: Zero boot_flags arg for calling board_init_f()

Copied from e83a7e94532 ("powerpc/mpc83xx: Zero boot_flags arg for
calling board_init_f()")

The argument boot_flags of board_init_f() is not used at all in the
powerpc specific board.c init sequence. Now with the generic init
sequence, this boot_flags arg is used by board_init_f().

This patch sets the r3 register that is used to pass the boot_flags
argument from the start.S board_init_f() call to 0 prior to the function
call to avoid unknown content to end up in gd->flags.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Fixes: 09f3ca3dd53 ("arm, powerpc: select SYS_GENERIC_BOARD")
diff --git a/arch/powerpc/cpu/mpc8xx/start.S b/arch/powerpc/cpu/mpc8xx/start.S
index 1f1107e..0aa73fc 100644
--- a/arch/powerpc/cpu/mpc8xx/start.S
+++ b/arch/powerpc/cpu/mpc8xx/start.S
@@ -171,6 +171,7 @@
 	lis	r3, CONFIG_SYS_IMMR@h
 	bl	cpu_init_f	/* run low-level CPU init code     (from Flash)	*/
 
+	li	r3, 0		/* clear boot_flag for calling board_init_f */
 	bl	board_init_f	/* run 1st part of board init code (from Flash) */
 
 	/* NOTREACHED - board_init_f() does not return */