mtd: spi-nor: atmel: remove global protection flag

This is considered bad for the following reasons:
 (1) We only support the block protection with BPn bits for write
     protection. Not all Atmel parts support this.
 (2) Newly added flash chip will automatically inherit the "has
     locking" support and thus needs to explicitly tested. Better
     be opt-in instead of opt-out.
 (3) There are already supported flashes which doesn't support
     the locking scheme. So I assume this wasn't properly tested
     before adding that chip; which enforces my previous argument
     that locking support should be an opt-in.

Remove the global flag and add individual flags to all flashes which
supports BP locking. In particular the following flashes don't support
the BP scheme:
 - AT26F004
 - AT25SL321
 - AT45DB081D

Please note, that some flashes which are marked as SPI_NOR_HAS_LOCK just
support Global Protection, i.e. not our supported block protection
locking scheme. This is to keep backwards compatibility with the
current "unlock all at boot" mechanism. In particular the following
flashes doesn't have BP bits:
 - AT25DF041A
 - AT25DF321
 - AT25DF321A
 - AT25DF641
 - AT26DF081A
 - AT26DF161A
 - AT26DF321

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20201203162959.29589-4-michael@walle.cc