x86/apic: Provide static call infrastructure for APIC callbacks

Declare and define the static calls for the hotpath APIC callbacks. Note
this deliberately uses STATIC_CALL_NULL() because otherwise it would be
required to have the definitions in the 32bit and the 64bit default APIC
implementations and it's hard to keep the calls in sync. The other option
would be to have stub functions for each callback type. Not pretty either

So the NULL capable calls are used and filled in during early boot after
the static key infrastructure has been initialized. The calls will be
static_call() except for the wait_irc_idle() callback which is valid to be
NULL for X2APIC systems.

Update the calls when a new APIC driver is installed and when a callback
override is invoked.

Export the trampolines for the two calls which are used in KVM and MCE
error inject modules.

Test the setup and let the next step convert the inline wrappers to make it
effective.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Juergen Gross <jgross@suse.com> # Xen PV (dom0 and unpriv. guest)

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