powerpc: Replace lxvd2x/stxvd2x with lvx/stvx in P7's memcpy/memmove

POWER9 DD2.1 and earlier has an issue where some cache inhibited
vector load traps to the kernel, causing a performance degradation.  To
handle this in memcpy and memmove, lvx/stvx is used for aligned
addresses instead of lxvd2x/stxvd2x.

Reference: https://patchwork.ozlabs.org/patch/814059/



	* sysdeps/powerpc/powerpc64/power7/memcpy.S: Replace
	lxvd2x/stxvd2x with lvx/stvx.
	* sysdeps/powerpc/powerpc64/power7/memmove.S: Likewise.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

(cherry picked from commit 63da5cd4)