ARM: davinci: da850 EVM: read mac address from SPI flash

DA850/OMAP-L138 EMAC driver uses random mac address instead of
a fixed one because the mac address is not stuffed into EMAC
platform data.

This patch provides a function which reads the mac address
stored in SPI flash (registered as MTD device) and populates the
EMAC platform data. The function which reads the mac address is
registered as a callback which gets called upon addition of MTD
device.

NOTE: In case the MAC address stored in SPI flash is erased, follow
the instructions at [1] to restore it.

[1] http://processors.wiki.ti.com/index.php/GSG:_OMAP-L138_DVEVM_Additional_Procedures#Restoring_MAC_address_on_SPI_Flash



Modifications in v2:
Guarded registering the mtd_notifier only when MTD is enabled.
Earlier this was handled using mtd_has_partitions() call, but
this has been removed in Linux v3.0.

Modifications in v3:
a. Guarded da850_evm_m25p80_notify_add() function and
   da850evm_spi_notifier structure with CONFIG_MTD macros.
b. Renamed da850_evm_register_mtd_user() function to
   da850_evm_setup_mac_addr() and removed the struct mtd_notifier
   argument to this function.
c. Passed the da850evm_spi_notifier structure to register_mtd_user()
   function.

Modifications in v4:
Moved the da850_evm_setup_mac_addr() function within the first
CONFIG_MTD ifdef construct.

Signed-off-by: Rajashekhara, Sudhakar <sudhakar.raj@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Cc: stable@kernel.org