FreeBSD/src 5fca1d9 (r324920)sys/amd64/amd64 pmap.c, sys/arm/arm pmap-v6.c

Fix the VM_NRESERVLEVEL == 0 build.

Add VM_NRESERVLEVEL guards in the pmaps that implement transparent
superpage promotion using reservations.

Reviewed by:    alc, kib
MFC after:      1 week
Differential Revision:  https://reviews.freebsd.org/D12764
DeltaFile
+15-0sys/amd64/amd64/pmap.c
+11-0sys/i386/i386/pmap.c
+7-0sys/arm/arm/pmap-v6.c
+6-0sys/arm64/arm64/pmap.c
+39-04 files

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