iio:adc:max1363 support SMBus for 8-bit devices

The driver currently supports only I2C access. But supported devices with an
accuracy of 8-bit are compatible with the SMBus byte access routines.

This patch wraps the send and receive routines depending on the chip
accuracy and fonctionnalities of its adapter.

For instance, this allows us to use a MAX11603 on a ICH7 controller.

This patch also simplifies the max1363_write_basic_config() routine to
use the struct max1363_state fields directly.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>