envsetup: Fix installrecovery for new fstab format

Change-Id: I26ab441c28350cce70bb976b249b16c6b83ab8da
build: Cleanup CPU-specific optimizations

 * TARGET_ARCH_CPU_VARIANT was a Linaro thing. Now that Android
   introducted TARGET_CPU_VARIANT, we should use this instead.
 * Added CFLAGS for Krait and Scorpion after the cleanup.

Change-Id: Iafb40ecefa353a1169c22601be4ce80069c3f587