gallium: Remove ppc asm backend

gallium: Remove ppc asm backend

The vs part hasn't been wired up since tgsi_sse2 was disabled in:

    commit 4eb3225b38ce12cb34ab3d90804c9683bd7b4ed3
    Author: José Fonseca <jose.r.fonseca@gmail.com>
    Date:   Tue Nov 8 00:10:47 2011 +0000

	Remove tgsi_sse2.

And it would certainly not work correctly in its current state:

draw/draw_vs_ppc.c: In function ‘draw_create_vs_ppc’:
draw/draw_vs_ppc.c:190:24: warning: assignment from incompatible pointer
type [enabled by default]

As with the sse2 backend, this should be done in llvm anyway.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>