sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Add .cfi_{start,end}proc for RISC-V assembly functions

This allows GDB to print more useful backtraces when setting a breakpoint
on an assembly function.

Reviewed By: jhb
Differential Revision: https://reviews.freebsd.org/D27177

Fix global pointer relaxations in the RISC-V kernel

The gp register is intended to used by the linker as another means of
performing relaxations, and should point to the small data section (.sdata).

Currently gp is being used as the pcpu pointer within the kernel, but the more
appropriate choice for this is the tp register, which is unused.

Swap existing usage of gp with tp within the kernel, and set up gp properly
at boot with the value of __global_pointer$ for all harts.

Additionally, remove some cases of accessing tp from the PCB, as it is not
part of the per-thread state. The user's tp and gp should be tracked only
through the trapframe.

Reviewed by: markj, jhb
Approved by: markj (mentor)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D19893

Permit supervisor to access user VA space for certain functions only.

This is done by setting SUM (permit Supervisor User Memory access)
bit in sstatus register.

The functions we allow access for are routines in assembly that
explicitly handle crossing the user kernel boundary.

Approved by: re (kib)
Sponsored by: DARPA, AFRL

o Add support for long double.
o Add support for latest RISC-V GNU toolchain.

Sponsored by: DARPA, AFRL
Sponsored by: HEIF5

Access pcpup using gp register.

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