cmd: loadb: Disable by default on sunXi

The sunXi arm64 build has overflown, leading to the main U-boot binary
overwriting the environment when flashing the new image, or even worse,
overwriting itself when we're calling saveenv.

Disable this command that is not critical until we can adress the issue
properly.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: NJagan Teki <jagan@openedev.com>

cmd/Kconfig

@@ -748,6 +748,7 @@ config CMD_I2C
 
 config CMD_LOADB
 	bool "loadb"
+	default n if ARCH_SUNXI
 	default y
 	help
 	  Load a binary file over serial line.