Rename Log2 and add IsPow2 to MathUtils for future use

Also remove unused pow2/pow2f functions.
JIT64: optimize multiplication by immediate constants

Factor out common code and handle a few more common cases.
JIT64: optimize rlwinmx/rlwinix and friends

Take advantage of movzx as a replacement for anding with 0xff or 0xffff, and
abuse loads from the register cache to save ops.
JIT64: Optimize cmpXX

Use TEST instead of CMP if we're comparing against 0 (rather common), and
optimize the case of immediate compares further.
JIT64: optimize sign/zero-extend

Also remove some comments that no longer apply since x86_32 was dropped.
JIT64: avoid using LEA for adds when not necessary
JIT64: use LEA for the "a = b + imm" case of addi
JIT64: use xor instead of mov for loading a zero regcache immediate
JIT64: tweak srwx/slwx BindToRegister arguments

Register B gets immediately moved into the shift register, so even if a == b
it doesn't need to be loaded.
JIT64: Optimize carry handling

Carries are rather common and unpredictable, so do them branchlessly wherever
we can.
JIT64: optimize some special cases of srawix

Shift by 31 and 1, both of which are pretty common, can be done in a few less
instructions. Tested with a hwtest.
JIT64: support merged branching for rlwinmx, too

Not quite as common a branch instruction as cmpwi, but close.
JIT64: optimize carry calculations

Omit carry calculations that get overwritten later in the block before they're
used. Very common in the case of srawix and friends.
Don't switch to a vertex array object of 0.

This causes glDrawArrays to fail in core profile, and thus on OS X, see:

http://renderingpipeline.com/2012/03/attribute-less-rendering/

There must be something bound, even though it is not used.

Fixes #7599.  I'm not sure this is actually the best way to fix it,
since AFAICT it makes a nonobvious assumption that *something* will be
bound before the first attributeless rendering in
TextureConverter::DecodeToTexture, but it's what degasus suggested and
seems to work.
Re-implement hiding of the menubar in fullscreen with render to main.
Added code to patch the codehandler's MMIO address to the currently running system.  Added code to detect the location of where the code list should be.  This allows any Gecko code handler to be used.  Replace the codehandler.bin file with the code handler to be used (e.g. codehandleronly.bin).
x64Emitter: add BMI1/BMI2 support

TZCNT and LZCNT use a completely different encoding scheme, so they should
probably go in a separate patch.

Also add some tests.
Common: Remove unnecessary define check in Log2
Merge pull request #956 from lioncash/preproc-stuff

Common: Remove unnecessary define check in Log2
Merge pull request #868 from FioraAeterna/bmi

x64Emitter: add BMI1/BMI2 support