[AGPGART] agp-amd64: section mismatches with HOTPLUG=n

When CONFIG_HOTPLUG=n, agp_amd64_resume() calls nforce3_agp_init(),
which is __devinit == __init, so has been discarded and is not
usable for resume.

WARNING: drivers/char/agp/amd64-agp.o - Section mismatch: reference to .init.text: from .text between 'agp_amd64_resume' (at offset 0x249) and 'amd64_tlbflush'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Dave Jones <davej@redhat.com>