refactor(gicv3): add helper function to get the limit of ESPI INTID

Add helper function gicv3_get_espi_limit() to get the value of
(maximum extended SPI INTID + 1), so that some duplicated code can be
removed later.

Signed-off-by: Heyi Guo <guoheyi@linux.alibaba.com>
Change-Id: I0355ca2647f872e8189add259f6c47d415494cce
2 files changed