power: supply: bd71828: Support wider register addresses

The BD71828 power-supply driver assumes register addresses to be 8-bit.
The new BD72720 will use stacked register maps to hide paging which is
done using secondary I2C slave address. This requires use of 9-bit
register addresses in the power-supply driver (added offset 0x100 to
the 8-bit hardware register addresses).

The cost is slightly used memory consumption as the members in the
struct pwr_regs will be changed from u8 to unsigned int, which means 3
byte increase / member / instance.
This is currently 14 members (expected to possibly be increased when
adding new variants / new functionality which may introduce new
registers, but not expected to grow much) and 2 instances (will be 3
instances when BD72720 gets added).

So, even if the number of registers grew to 50 it'd be 150 bytes /
instance. Assuming we eventually supported 5 variants, it'd be
5 * 150 bytes, which stays very reasonable considering systems we are
dealing with.

As a side note, we can reduce the "wasted space / member / instance" from
3 bytes to 1 byte, by using u16 instead of the unsigned int if needed. I
rather use unsigned int to be initially prepared for devices with 32 bit
registers if there is no need to count bytes.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patch.msgid.link/57c87f7e2082a666f0adeafcd11f673c0af7d326.1765804226.git.mazziesaccount@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>