Build failure - port amd64

[Paul Goyette <paul%whooppee.com@localhost>]

It seems that the latest changes related to drm have broken the build 
for the INSTALL kernel:

#      link  INSTALL/netbsd
/build/netbsd-local/tools/x86_64/amd64/bin/x86_64--netbsd-ld -Map netbsd.map 
--cref -T /build/netbsd-local/src/sys/arch/amd64/conf/kern.ldscript -Ttext 
0xffffffff80100000 -e start -X -o netbsd ${SYSTEM_OBJ} ${EXTRA_OBJ} vers.o
drm_memory.o: In function `drm_mtrr_add':
drm_memory.c:(.text+0x3f): undefined reference to `mtrr_funcs'
drm_memory.o: In function `drm_mtrr_del':
drm_memory.c:(.text+0x7b): undefined reference to `mtrr_funcs'
*** [netbsd] Error code 1
1 error


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