Revert "libm: Enable fast pow(), memmove, memcmp, and memset for all NEON-capable devices"

This reverts commit 834821a30da45aa6b9a5bd45ae80c40c526c3634.
libm: Enable fast pow(), memmove, memcmp, and memset for all NEON-capable devices

Change-Id: I2d9008f220bc634579628407a56d8c04816a9578