bsd-user:Add AArch64 register handling and related functions

bsd-user:Add AArch64 register handling and related functions

Added header file for managing CPU register states in FreeBSD user mode.
Introduced prototypes for setting and getting thread-local storage (TLS).
Implemented AArch64 sysarch() system call emulation and a printing function.
Added function for setting up thread upcall to add thread support to BSD-USER.
Initialized thread's register state during thread setup.
Updated ARM AArch64 VM parameter definitions for bsd-user, including address spaces for FreeBSD/arm64 and
a function for getting the stack pointer from CPU and setting a return value.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Ajeet Singh <itachis@FreeBSD.org>
Co-authored-by: Jessica Clarke <jrtc27@jrtc27.com>
Co-authored-by: Sean Bruno <sbruno@freebsd.org>
Co-authored-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240707191128.10509-3-itachis@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>