audioflinger: Enable ARMv5TE optimized resampler

Previously, the optimized asm option is only enabled when
__ARM_ARCH_5E__ is defined, which is assigned in armv5te.mk
rather than armv7-a series targets.  This patch checks the ARM CPU
feature about half-word multiply instructions to enable ARMv5TE
resampler optimization routines properly.

Change-Id: I95a8b6212f2899c651b89f4a741410266085b5ec