Support boot Android image without address on bootm command

Support boot Android image without address on bootm command

It works perfectly fine to boot an Android boot.img with bootm command
followed by an explicit address argument that holds the image.  But if
we have boot.img downloaded into default 'loadaddr', and then boot it
using bootm command without the address argument, we will run into
problem, because U-Boot fails to find ramdisk and fdt (second area) in
boot.img.

The current Android image support assumes there is always an address
argument on bootm command.  However just like booting any other images,
'loadaddr' should be used when address argument is missing from bootm
command.  It patches boot_get_ramdisk() and boot_get_fdt() a bit to
support this quite common usage of bootm command for Android image.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>