x86/vlapic: express x2apic msr readability with a bitmap

x86/vlapic: express x2apic msr readability with a bitmap

The x2apic MSR space is currently defined between 0x800 and 0x83f, which
conveniently fits in a 64 bit wide bitmap.  This is far more efficient than
the cascade comparisons generated by the switch statement, which can't be
optimised because of the case ranges used for the ISR, TMR and IRR blocks.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Convert 0xffUL to ((1UL << (NR_VECTORS / 32)) - 1) and drop a couple of
clearly superfluous parentheses.

Signed-off-by: Jan Beulich <jbeulich@suse.com>