Alpha systems based on the "Laser" and "TurboLaser" system architecture
have an interesting feature: the RTC and console UART are present on each
CPU module, but only those peripherals on the "primary" CPU module matter,
because each CPU's module's periperals are mapped to the same physical
address, but are only accessible by that CPU module. The firmware selects
a primary CPU to boot the system, and that CPU's RTC and UART are the
system RTC and console, respectively.

To handle this, on systems where it's needed, we wrap the RTC gettime/settime
calls and, if not running on the primary CPU already, cross-call to the primary
to perform the RTC access.

Wrap the mcclock driver's mc146818_softc inside a new mcclock_softc.
This commit represents no functional change, but forms the basis for
a future functional change.

bus_space-ify.

tlsb -> gbus. No functional change.

Shuffle GBus-related files into their own directory in preparation for
other GBus attachments. No functional change here; just minimal editing
to reflect path differences after moving the files.

tlsb -> gbus. No functional change.

Shuffle GBus-related files into their own directory in preparation for
other GBus attachments. No functional change here; just minimal editing
to reflect path differences after moving the files.