mtd: spi-nor-core: Adding different type of command extension in Soft Reset

Power-on-Reset is a method to restore flash back to 1S-1S-1S mode from 8D-8D-8D
in the begging of probe.

Command extension type is not standardized across flash vendors in DTR mode.

For suiting different vendor flash devices, adding a flag to seperate types for
soft reset on boot.

Signed-off-by: JaimeLiao <jaimeliao.tw@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>