hwmon: (lm75) Hide register size differences in regmap access functions

Hide register size differences in regmap access functions to simplify
runtime code and to simplify adding support for I3C devices. Also
use regmap API functions for bit operations where possible.

For this to work, the 16-bit and 8-bit configuration register has to be
mapped to a 16-bit value. Unlike other registers, this register is a
low-byte-first register, presumably for compatibility with chips with
8-bit wide configuration registers. Hide the differences in the regmap
access code.

While at it, enable alarm attribute support for TMP112.

Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>