Switch to scheduler thread on timer (timeout) interrupts

Major:

Support for switching to scheduler thread of the current thread on timeout expiry. Scheduler thread is the thread associated with scheduler recv endpoint on cos_switch or cos_sched_asnd.

Minor:

VGA: It looks like the bare metal boot faults at random places with new ACPI/APIC changes and I could relate that to VGA driver, but haven't thoroughly debugged it. For now, allowing VGA printks only after paging_init. This is a workaround for now, need to debug the actual issue after the deadline.
Yet another bug in SL: sl_thd_wakeup_no_cs_rm API to not use CS or not remove thread from the timeout queue, this is required by sl_timeout_xxx api. sl_thd_wakeup_no_cs however is a wrapper around this with removal from timeout queue if thread was blocked on timeout.

Choose one (Mandatory):

[ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
[x] This PR is mature, and ready to be integrated into the repo.

@gparmer

As part of this pull request, I've considered the following:

[x] Comments adhere to the Style Guide (SG)
[x] Spacing adhere's to the SG
[x] Naming adhere's to the SG
[x] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
[ ] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

[x] I've made an attempt to remove all redundant code
[x] I've considered ways in which my changes might impact existing code, and cleaned it up
[x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
[x] I've commented appropriately where code is tricky
[x] I agree that there is no "throw-away" code, and that code in this PR is of high quality

I've tested the code using the following test programs (provide list here):

unit tests in implementation/tests
vkernel in implementation/no_interface
integrated in rump2cos env and basic tests with ping works fine. [There is one major problem which is not related to this PR but perhaps to using sl as vkernel scheduling, and I'm working on that problem -- at some point, system stops responding to pings. ]

gwsystems / composite