Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix switching to physical mode as part of calling into EFI runtime
services or PAL procedures. The new implementation is based on
specific functions that are known to be called in certain scenarios
only. This in particular fixes the PAL call to obtain information
about translation registers. In general, the new implementation does
not bank on virtual addresses being direct-mapped and will work when
the kernel uses PBVM.

When new scenarios need to be supported, new functions are added if
the existing functions cannot be changed to handle the new scenario.
If a single generic implementation is possible, it will become clear
in due time.

While here, change bootinfo to a pointer type in anticipation of
future development.