bsd-user: Add system independent stack, data and text limiting
Eliminate the x86 specific stack stuff in favor of more generic control
over the process size:
target_maxtsiz max text size
target_dfldsiz initial data size limit
target_maxdsiz max data size
target_dflssiz initial stack size limit
target_maxssiz max stack size
target_sgrowsiz amount to grow stack
These can be set on a per-arch basis, and the stack size can be set
on the command line. Adjust the stack size parameters at startup.
Signed-off-by: Stacey Son <sson@FreeBSD.org> Signed-off-by: Warner Losh <imp@bsdimp.com> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>