AArch64: Improve MIR to LIR translation for abs

Improve translation by using a shorter and more efficient sequence for integer
abs, and replacing UBFM with AND for FP abs in integer registers.

Change-Id: Ifc39cd7806ed637d5cfc3284c435b5d501047eb5
Signed-off-by: Alexandre Rames <alexandre.rames@arm.com>
4 files changed