misc: bphy: Add ioctl to get max irq number

commit c516399919a2b2295013aa8599241f65d025d90b from
git@git.assembla.com:cavium/WindRiver.linux.git

This patch aims at providing users of this driver with
maximum IRQ number via a ioctl call.

Signed-off-by: Jakub Palider <jpalider@marvell.com>
Change-Id: I9165517f5e056217f51cda43261810ac3e718de7
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/45891


Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Radha Chintakuntla <radhac@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <Sunil.Goutham@cavium.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/47713


Reviewed-by: Naveen Mamindlapalli <Naveen.Mamindlapalli@cavium.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>