x86/APIC: drop clustered_apic_check() hook

x86/APIC: drop clustered_apic_check() hook

The hook functions have been empty forever (x2APIC) or issuing merely a
printk() for a long time (xAPIC). Since that printk() is (a) generally
useful (i.e. also in the x2APIC case) and (b) would better only be
issued once the final APIC driver to use was determined, move (and
generalize) it into connect_bsp_APIC().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>