Now that we have an accurate CONFIG_64BIT describing sandbox bitness,
we don't need to assume everything except __x86_64__ as 32-bit.

This assumes that sizeof(long) == sizeof(void *), which is assumed
anyway throughout the code base.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>