drivers: flash: provide api to reset the flash registers

changes enable flash driver to provide api interface to send reset memory
spi command to the spi flash. The reset memory command would bring the
spi flash to its default power-on state and loose all the volatile register
settings.
Flash reset is needed when more than one controller access the flash chip
in a shared mode.

Signed-off-by: Deepti Deshatty <deepti.deshatty@intel.corp-partner.google.com>