hwmon: (spd5118) Add support for Renesas/ITD SPD5118 hub controllers

hwmon: (spd5118) Add support for Renesas/ITD SPD5118 hub controllers

The SPD5118 specification says, in its documentation of the page bits
in the MR11 register:

"
This register only applies to non-volatile memory (1024) Bytes) access of
SPD5 Hub device.
For volatile memory access, this register must be programmed to '000'.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
"

Renesas/ITD SPD5118 hub controllers take this literally and disable access
to volatile memory if the page selected in MR11 is != 0. Since the BIOS or
ROMMON will access the non-volatile memory and likely select a page != 0,
this means that the driver will not instantiate since it can not identify
the chip. Even if the driver instantiates, access to volatile registers
is blocked after a nvram read operation which selects a page other than 0.

To solve the problem, add initialization code to select page 0 during
probe. Before doing that, use basic validation to ensure that this is
really a SPD5118 device and not some random EEPROM.

Cc: Sasha Kozachuk <skozachuk@google.com>
Cc: John Hamrick <johnham@google.com>
Cc: Chris Sarra <chrissarra@google.com>
Tested-by: Armin Wolf <W_Armin@gmx.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>