Watchdog: sp5100_tco: Refactor MMIO base address initialization

Combine MMIO base address and alternate base address detection. Combine
based on layout type. This will simplify the function by eliminating
a switch case.

Move existing request/release code into functions. This currently only
supports port I/O request/release. The move into a separate function
will make it ready for adding MMIO region support.

Co-developed-by: Robert Richter <rrichter@amd.com>
Signed-off-by: Robert Richter <rrichter@amd.com>
Signed-off-by: Terry Bowman <terry.bowman@amd.com>
Tested-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220202153525.1693378-3-terry.bowman@amd.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>