[J-core] qemu updates / roadmap

[Christopher Friedt]

Some progress:

You can load the mimas_v2.bin boot rom file as a bios in Qemu, but a)
the size has to be increased in shix.c from 0x4000 to 0x8000 to
accomodate the 32 kB j-core boot rom size, and b) the initial program
counter and initial stack pointer need to be read into cpu->pc and
cpu->gregs[ 15 ] from address 0 and 4, respectively, after the boot
rom is loaded.

Use the following to run the bios.

qemu-system-sh4eb -m mimasv2 -bios mimas_v2.bin

Currently I cloned / modified shix.c with the changes above and just
renamed the file mimasv2.c

Still need to introduce sh7619.c, sh7619_regs.h, sh7619_regnames.h,
sh7619_regnames.c.
Still need to do a quick once over of the memory map, to make sure
it's sane-ish.
Still need to add e.g. the uartlite virtual device.
Still need to slightly modify the interrupt routine.

But yeah, I'm able to begin in _start, then jump out into _testjsr,
then jump back into _start, etc. I haven't spent too much time running
past there.

Cheers,

C