plat/common: Migrate the APIC implementation to the xPIC driver

plat/common: Migrate the APIC implementation to the xPIC driver

Introduce `arch/x86/x86_64/include/uk/asm/arch.h` for architectural
definitions of x86_64 and migrate APIC definitions into arch.

Migrate the driver implementation into `drivers/ukintctlr/xpic/`
The APIC ops are still accessible via the `apic` global.

Update the include guards of `apic.h`.

Update `plat/` to include `uk/intctlr/apic.h`. Update the KVM config
to enable `UKINTCTLR_XPIC` when compiling for x86_64.

Notice: Picking individual commits in this PR will break the build.

Signed-off-by: Michalis Pappas <michalis@unikraft.io>
Reviewed-by: Marco Schlumpp <marco@unikraft.io>
Reviewed-by: Sergiu Moga <sergiu@unikraft.io>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
GitHub-Closes: #1103