regmap: Introduce max_raw_read/write for regmap_bulk_read/write

There are some buses which have a limit on the maximum number of bytes
that can be send/received. An example for this is
I2C_FUNC_SMBUS_I2C_BLOCK which does not support any reads/writes of more
than 32 bytes. The regmap_bulk operations should still be able to
utilize the full 32 bytes in this case.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>