Pass the bsd_param into loader_exec, and adjust. We use it to track the
inital stack allocation and to set stack, open files, and other state
shared between bsdload.c and elfload.c

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>