mips_malta: fix BIOS endianness swapping

mips_malta: fix BIOS endianness swapping

If the target is little endian (mipsel) then the BIOS image endianness
is swapped so that the big endian BIOS binaries commonly produced can be
loaded correctly.

When using the -bios argument the BIOS is loaded using
load_image_targphys, however this doesn't perform the load to target
memory immediately. Instead it loads the BIOS file into a struct Rom
which will later be written to target memory upon reset. However the
endianness conversion was being performed before this, on init, and
operating on the target memory which at this point is blank & will later
be overwritten by the (big endian) BIOS image. Correct this by operating
on the data referenced by struct Rom rather than the target memory when
the -bios argument is used.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>