Add support for MediaTek Images:

-- Unpack and repack boot/recovery images.
-- Append proper headers to ramdisk when repacking.
-- Compiled mkimage to assist with the headers.

-- This support currently does not include the logo images at this time.

-- MT6516
-- MT65x3 (MT6513 and MT6573)
-- MT65x5 (MT6515 and MT6575)
-- MT6577
-- MT65x2 (MT6572 and MT6582)
-- MT6589
-- MT83xx (MT8377 and MT8389)