mtd: spi-nor-core: Track flash's internal address mode

The nor->addr_width tracks number of address bytes used in
read/program/erase ops and eventually set to 4 for >16MB chips, regardless
of flash's internal address mode. For Infineon SEMPER flash's, we use
Read/Write Any Register commands for configuration and status check.
These commands take 3- or 4-byte address depending on flash's internal
address mode.

Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>