Revert "build: Don't work around cortex-a8 issues when targeting a9 only"

This reverts commit 9facada1cf44ef1c2e3f7ad2bba60b430182e526.
build: armv7-a-neon: set '-m' options for all variants

**use -march -mtune combo for targets we build for
   (snapdragons aren't real cortex* cpus)
**treat krait as a15
**don't fix cortex-a8 on higher variants

Signed-off-by: helicopter88 <johnlemon.lol@gmail.com>
Signed-off-by: Andrew Sutherland <dr3wsuth3rland@gmail.com>
Change-Id: Ic384193181d2162f533aed206f3c40fcee3dee92