cfi_flash: Enable PPB protection for all AMD cmdset flash chips

Not only Spansion supports the Persistent Protection Bits (PPB) locking.
Other devices like the Micron JS28F512M29EWx also support this type
of locking/unlocking. Detection of support is done in the same way as
done for the Spansion chips - via the 0x49 CFI word.

This patch enables this PPB protection mechanism for all AMD type
(AMD commandset) chips.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Holger Brunck <holger.brunck@keymile.com>
Tested-by: Holger Brunck <holger.brunck@keymile.com>