The 23:16 bits in the IOAPIC version register is the highest entry in the I/O
redirection table, which is 1 smaller than the number of interrupt input
pins. But currently we use these bits directly as the number of pins.
This patch abstracts the pin count calculation code and adds 1 to the max rte
entry number to get the right pin count.
Signed-off-by: Junjie Mao <junjie.mao@intel.com>