FreeBSD/src 68c7542 (r338858)sys/amd64/amd64 support.S

amd64: even up copyin/copyout with memcpy + other cleanup

- _fault handlers for both primitives are identical, provide just one
- change the copying scheme to match memcpy (in particular jump
avoidance for the most common case of multiply of 8)
- stop re-reading pcb address on exit, just store it locally (in r9)

Reviewed by:    kib
Approved by:    re (gjb)
Differential Revision:  https://reviews.freebsd.org/D17265
DeltaFile
+30-26sys/amd64/amd64/support.S
+30-261 files

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