fmcdio_vhdci_eem: refactor

This allows access to the pin allocation from kernels, which becomes useful
to configure the direction shift register.

artiq/coredevice/fmcdio_vhdci_eem.py

@@ -0,0 +1,6 @@
+eem_fmc_connections = {
+    0: [0, 8, 2, 3, 4, 5, 6, 7],
+    1: [1, 9, 10, 11, 12, 13, 14, 15],
+    2: [17, 16, 24, 19, 20, 21, 22, 23],
+    3: [18, 25, 26, 27, 28, 29, 30, 31],
+}