bsd-user:Add CPU initialization and management functions

bsd-user:Add CPU initialization and management functions

Added function to initialize ARM CPU and check if it supports 64-bit mode.
Implemented CPU loop function to handle exceptions and emulate execution of instructions.
Added function to clone CPU state to create a new thread.
Included AArch64 specific CPU functions for bsd-user to set and receive thread-local-storage
value from the tpidr_el0 register.
Introduced structure for storing CPU register states for BSD-USER.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Ajeet Singh <itachis@FreeBSD.org>
Co-authored-by: Kyle Evans <kevans@freebsd.org>
Co-authored-by: Sean Bruno <sbruno@freebsd.org>
Co-authored-by: Jessica Clarke <jrtc27@jrtc27.com>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240707191128.10509-2-itachis@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>