pegbox: exec_init: remove scheduler test code now it's known working
Defined a peripheral bus (pegbus) and implemented it in pegasus
pegbox: Implement basic pegbus interrupt handler
pegbox: implement pegbus driver registration and a dummy driver for 0xff0d
pegbox: debug: fix BUILD_BUG_ON output to avoid confusing negation
pegbox: implement kprint_half_hex (just prints low nybble of A)
pegbox: pegbus: use half_hex for slot IDs

Also renamed the 'dummy' driver to 'test_device'.