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

MFC r258247, r258250, r258257

Remove a pointless #ifdef AIM. This is just PPC64 specific, including
64-bit Book-E.

Make single precision floating point arithmetic actually work

Split the function of the PCB_FPU flags into two: PCB_FPU now indicates that
the actual FPU is enabled, while PCB_FPREGS indicates that the FPU state
structure in the PCB is valid.

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

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

/* -> /*- for license, minor formatting changes

Don't include sys/user.h merely for its side-effect of recursively
including other headers.

Invalide pcb's fpu cpu # by setting it to INT_MAX, not NULL.

Use __FBSDID rather than rcsid[].

Enable the FPU on first use per-thread and save state across context
switches. Not as lazy as it could be. Changing FPU state with sigcontext
still TODO.

fpu.c - convert some asm to inline C, and macroize fpu loads/stores
swtch.S - call out to save/restore fpu routines
trap.c - always call enable_fpu, since this shouldn't be called once
the FPU has been enabled for a thread
genassym.c - define for pcb fpu flag

Fix commenting around NetBSD version string.

FPU support.

Obtained from: NetBSD (portions)