MFC r329859,r329860: Float protection in stand

r329859: Do not include float interfaces when using libsa.

We don't support float in the boot loaders, so don't include
interfaces for float or double in systems headers. In addition, take
the unusual step of spiking double and float to prevent any more
accidental seepage.

r329860: Floaty McFloatface is funnier...

MFC r313194:
Define the vm_ooffset_t and vm_pindex_t types as machine-independend.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Import RISC-V machine headers. This is a minimal set required to compile
kernel and userland.

Reviewed by: andrew, imp, kib
Sponsored by: DARPA, AFRL
Sponsored by: HEIF5
Differential Revision: https://reviews.freebsd.org/D4554