[no subject]

[Myrtle Shah]

These are some initial patches to bugs I found attempting to
get a XIP kernel working on hardware:
 - 32-bit VexRiscv processor
 - kernel in SPI flash, at 0x00200000
 - 16MB of RAM at 0x10000000
 - MMU enabled
 
I still have some more debugging to do, but these at least
get the kernel as far as initialising the MMU, and I would
appreciate feedback if anyone else is working on RISC-V XIP.