Revert "agp: AMD AGP is used on UP1100 & UP1500 alpha boxen"

This reverts commit f191f144

.

The AMD 751 and 761 chipsets are used on the UP1000, UP1100, and UP1500
OEM motherboards, but they neglect to do anything to make AGP work.

According to Ivan Kokshaysky:
There is quite fundamental conflict between the Alpha architecture and
x86 AGP implementation - Alpha is entirely cache coherent by design,
while x86 AGP is not (I mean native AGP DMA transactions, not a PCI over
AGP). There are no such things as non-cacheable mappings or software
support for cache flushing/invalidation on Alpha, so x86 AGP code won't
work on Nautilus.

So there's no point in allowing this driver to be configured on Alpha.

Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>