The roundup_pow_of_two function is making use of __roundup_pow_of_two
when the call to __builtin_constant_p fails, which is not implemented in
barebox.
Copied the code from Linux log2.h header.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>