nand: start figuring out nand pins

This is the first step towards figuring out how the nand pins work.  We
have identified the "Run Command" register as well as the "NAND Address"
registers.  We do not yet know the full command set, nor do we know how
it decides where to get data from.
debugger: add ext_op command

This will allow us to figure out how the ext_op 0xa5 opcode works.
nand: buffer data reads/writes and print out grouped

This groups all NAND reads and writes together, based on ctrl
information.  The downside here is that timestamp information is lost.
readme: add more special function registers

Also add more description of the chip.
debugger: add memset

Add a slow-but-steady memset command, useful for testing the ECC
algorithm.