aspeed: i2c: Use reg array instead of individual vars

aspeed: i2c: Use reg array instead of individual vars

Using a register array will allow us to represent old-mode and new-mode
I2C registers by using the same underlying register array, instead of
adding an entire new set of variables to represent new mode.

As part of this, we also do additional cleanup to use ARRAY_FIELD_
macros instead of FIELD_ macros on registers.

Signed-off-by: Joe Komlodi <komlodi@google.com>
Change-Id: Ib94996b17c361b8490c042b43c99d8abc69332e3
[ clg: use of memset in aspeed_i2c_bus_reset() ]
Message-Id: <20220331043248.2237838-5-komlodi@google.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>