ubee,devfd: add device select support for port 0x58

It's probably not present but it costs us nothing much to support
ubee,devhd: Bring more into line with what is needed

Minor 4-7 are the floppy devices on the WD1002-5 and for those we must set the
side bit in port 0x48

Implement the 0x58 device select logic

Check the device is present on open
ubee: More work on the disk controllers

Set the WD1002 up correctly for and work in 512 bytes/sector mode. This should
bring the devhd side roughly where we need it. This doesn't deal with the
precomp values (can we trust the firmware?) or disk step rates (can we read
the firmware set values somewhere ?)
ubee: Further floppy driver bashing

512 bytes/sector, double sided

Also set the step to 6ms
ubee,devhd: step rates and the like
trs80: Set a 2ms seek time on the hard disk
ubee: enable CRTC loading

Load the CRTC up for 80x25 mode using the table given in the 256TC manuals
ubee: clean up some remaining TRS80isms
process: note problem to look at wrt ubee and 64 ticks/second
timer: add initial support for RTC seconds locking

We don't try and use the RTC as our actual clock. Many RTCs are not Y2K safe
or have their own interesting sets of problems. We would also have to keep
doing Unix type v RTC time conversion maths.

Instead we treat the RTC seconds as a free running counter and update our
second tick as we see the RTC one shift. This also gives us up to 59 seconds
of 'overrun' which should do for the worst case disk I/O problems.
ubee: 64 ticks/second and turn on the RTC

We'll need the RTC in fact as 64 doesn't divide by 10
trs80: turn on the RTC support
trs80: CRTC reg 0 was not being set

Backported from Microbee port
nc100: add RTC support
trs80: ensure the rtc digit wrap doesn't catch us out
z80pack: add rtc helper
z80pack: fix vt.c build failure
z80pack: turn on RTC support
z80pack-lite: add RTC support
PORTING: some updates