powerpc: Remove assembly versions of strcpy, strcat, strlen and strcmp

A number of our assembly implementations of string functions do not
align their hot loops. I was going to align them manually, but I
realised that they are are almost instruction for instruction
identical to what gcc produces, with the advantage that gcc does
align them.

In light of that, let's just remove the assembly versions.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>