armv7-a-neon: cleanup and fix cpu variant detection

Summary:
Fixes armv5te defaults for anything other than cortex-a7, cortex-a9,
cortex-a15, or krait.

Test Plan: verify on grouper

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D195

Conflicts:
	core/combo/arch/arm/armv7-a-neon.mk