i2c: nomadik: use bitops helpers

Constant register bit fields are declared using hardcoded hex values;
replace them by calls to BIT() and GENMASK(). Replace custom GEN_MASK()
macro by the generic FIELD_PREP(). Replace manual bit manipulations by
the generic FIELD_GET() macro.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>