iio: mlx90614: Factor our register IO and constants into model specific descriptor

Factor out all the differences between MLX90614 and other similar chips
into a structure which describes the chip and allows abstracting out the
differences from the driver code. No functional change.

This patch moves all the RAM and EEPROM IO opcodes into the descriptor
structure and combines them, instead of combining the opcode and offset
in macros.
Acked-by: Crt Mori <cmo@melexis.com>
Tested-by: Crt Mori <cmo@melexis.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20230510102251.10118-5-marex@denx.deSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>