This patch adds the memory card pins to the M1 platform definition in
mibuild.
I've tentatively named them "mmc". As far as I can tell, "MMC" is not
trademarked ("MultiMediaCard" the new "eMMC" would be), and "MMC" is
commonly used in the industry in a descriptive way to refer to this
sort of interface.
The original Verilog-based M1 calls the interface "mc", but since
several names have changed between milkymist and -ng, I thought I'd
use a more familiar name.
Usage example (clock signal divided by powers of two on the MMC TPs):
https://github.com/wpwrak/ming-ddc-debug/blob/counter-on-mmc/build.py
- Werner
