arm: apple: Switch to standard boot

Use standard boot instead of the distro boot scripts. Use
BOOTSTD_FULL instead of BOOTSTD_DEFAULTS for easier interactive use.

Signed-off-by: Janne Grunau <j@jannau.net>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Neal Gompa <neal@gompa.dev>