Scheduler will now set a timer interrupt deadline for when it should get
interrupted next. This fixes a big issue I've had for a long time where
sleeping on an idle core would have to wait for the next periodic
interrupt to wake up. This could cause 1 ms sleeps to be close to 10 ms.
This currently only supports lapic timers and will still fallback to
periodic interrupts when running with PIC. I should add deadline support
to PIT/HPET but why would you run with APIC disabled ;)
Stack pointer was pointing to value of return address on return instead
of past it. This did not affect anything as ig Processor::yield() didn't
use stack after calling the trampoline
Doing a yield no longer raises a software interrupt. Instead it just
saves all the callee saved registers, ip, sp and return value. Because
yield is only called in the kernel, it can just restore registers and
jump to the target address. There is never a need to use iret :)
