bsd-user/arm/target_arch_vmparam.h: Parameters for arm address space

bsd-user/arm/target_arch_vmparam.h: Parameters for arm address space

Various parameters describing the layout of the ARM address space. In
addition, define routines to get the stack pointer and to set the second
return value.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>