kernel: mtd: limit Macronix lock feature to MX25L6405D only

kernel: mtd: limit Macronix lock feature to MX25L6405D only

Though most Macronix Flash support the lock feature, the generic lock
implementation is not fully compatible with the Macronix series Flash.
Enabling the lock feature globally is unsafe. These hack patches are
used to unlock the Flash of ubnt devices on the ath79 target. Rework
these patches and move it to the ath79 target to prevent the potential
risk.

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/21754
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>