mtd: add lock fixup for AT49BV640D and AT49BV640DT chips

This patch sets the MTD_POWERUP_LOCK flag for AT49BV640D and AT49BV640DT
devices, since the devices are locked when powered up and needs to be unlocked
before interfaced.

Quote datasheet; "At power-up and reset, all sectors have their Softlock
protection mode enabled.".

Tested on AVR32 hardware platform with an AT49BV640D flash device.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>