generic: Create generic board infrastructure and move misc.h to it

Instead of creating a misc.h file in each board directory, create a
generic board directory and declare misc.h there.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/simulator/Makefile

@@ -1,3 +1,4 @@
 # Additional simulator build rules
 
 src-y += simulator/main.c simulator/gpio.c
+src-y += generic/crc16_ccitt.c generic/alloc.c