Sort out build flags

[Famicoman]

I've learned that specifying -marc and -mtune is redundant and -mcpu can be used alone. Explicitly setting -marm is still a good idea as it forces use over -mthumb which supplies backwards compatability for 16-bit platforms.

[darkdrgn2k]

Some notes
For 64 bit arm boars no parameters are needed as acceleration is automatic.

Also it almost seems like the amount of performance gained by any other flag (if any) is negligible. Simply adding acceleration for arm7 boards is enough. The binary seems to run on any arm7 board.