watchdog: aspeed: add support for dual boot

Set WDT_CLEAR_TIMEOUT_AND_BOOT_CODE_SELECTION into WDT_CLEAR_TIMEOUT_STATUS
to clear out boot code source and re-enable access to the primary SPI flash
chip while booted via wdt2 from the alternate chip.

AST2400 datasheet says:
"In the 2nd flash booting mode, all the address mapping to CS0# would be
re-directed to CS1#. And CS0# is not accessible under this mode. To access
CS0#, firmware should clear the 2nd boot mode register in the WDT2 status
register WDT30.bit[1]."

Signed-off-by: Ivan Mikhaylov <i.mikhaylov@yadro.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20190828102402.13155-4-i.mikhaylov@yadro.com


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