x86/apic: Get rid of get_physical_broadcast()

There is no point for this function. The only case where this is used is
when there is no XAPIC available, which means the broadcast address is 0xF.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240212154639.057209154@linutronix.de