ARM: 4-byte align start of all asm functions

Due to apprent bugs in the GNU assembler and/or linker, relocations
can be incorrectly processed if the alignment of a Thumb instruction
is changed in the output file compared to the input object.

This fixes crashes in h264 decoding with Thumb enabled. No effect in
ARM mode since everything is 4-byte aligned there.

Signed-off-by: Mans Rullgard <mans@mansr.com>
