Use register numbers instead of register names

Use register numbers instead of register names

Avoid ambiguity by using register numbers. Register names are
interpreted depending on the ABI. Fixes the issue with mips64 gcc,
where registers t0-t4 are translated into $8-$11 (o32 ABI) instead
of $12-$15 (o64 ABI).

Also, use t9 ($25) for storing function address
(in getProcAddress.cpp).

Change-Id: I12ef5cd98bf14dab3c01f2756889cc02856c1cd8