GXemul Code2

Adding skeq and skne instruction implementations.

Various CHIP8 updates.

Implementing a CHIP8 cpu mode, and a corresponding CHIP8
machine, for fun. Disassembly support for all instructions,
and most of the common instructions have been implemented:
mvi, mov_imm, add_imm, jmp, rand, cls, sprite, skeq_imm, jsr,
skne_imm, bcd, rts, ldr, str, mov, or, and, xor, add, sub,
font, ssound, sdelay, gdelay, and bogus skup/skpr.
(No support for actual sound yet, and no keyboard stuff.)

Minor updates to the LCA PCI controller.

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Adding bogus SCSI commands 0x51 (SCSICDROM_READ_DISCINFO) and
0x52 (SCSICDROM_READ_TRACKINFO) to the SCSI emulation layer,
to allow NetBSD/pmax 4.0_BETA to be installed from CDROM.

Continuing on the timer stuff: experimenting with MIPS count / compare interrupts connected to the timer framework.

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Continuing on the LCA PCI bus controller (for Alpha machines).

Adding a FreeBSD development specific YAMON environment variable ("khz") (as suggested by Bruce M. Simpson). Moving YAMON environment variable initialization from machine_evbmips.c into promemul/yamon.c, and adding some more variables.