ARM: imx: romapi: Fix signed integer bitwise ops misuse

Bitwise operations on signed integers are not defined,
replace them with per-call checks.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>