On my Lenovo laptop, the firmware maps the EFI framebuffer with MTRRs set
to uncacheable. This leads to execrable console performance. Once PMAP is
up, remap the framebuffer as write-combining. This reduces boot time on my
laptop by 60% when booting with EFI.

MFC after:	2 weeks
Bump mdoc date after r268621.

X-MFC-With:	r268621