flashchips: Add Macronix MX25U51245G

Copy 'n paste support for Macronix MX25U51245G. I don't pretend to know
a whole lot about SPI FLASH so its mostly copied from other MX25U devices
and double checked a few bits and pieces against the datasheet.

I have tested basic probe, read, erase and write using layout files. I
tested both with 4MB@0x0000000 and 64K0@0x3f00000 (the later means I
have tested 4-byte addressing).

Change-Id: I2117fc205006088967f3d97644375d10db1791f1
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-on: https://review.coreboot.org/26949
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
2 files changed