ISX iM1283 is a "simple eDP signal generator" which utilizes a XC7A100T
FPGA, and come with a header populated with the FPGA's JTAG.
This commit adds initial reverse engineered IOs including the DDR3 DRAM
(which cannot work reliably @ DDR3-800, so the system clock is defaultly
set to 80MHz now), two LEDs and SD slot.
Signed-off-by: Icenowy Zheng <uwu@icenowy.me>