i2c: xlp9xx: Add support for SMBAlert

i2c: xlp9xx: Add support for SMBAlert

Add support for SMBus alert mechanism to i2c-xlp9xx driver.
The second interrupt is parsed to use for SMBus alert.
The first interrupt is the i2c controller main interrupt.

BugLink: https://launchpad.net/bugs/1786981
Signed-off-by: Kamlakant Patel <kamlakant.patel@cavium.com>
Signed-off-by: George Cherian <george.cherian@cavium.com>
Reviewed-by: Jan Glauber <jglauber@cavium.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
(cherry picked from commit 40f4e372cba8a6729c997c0bda1fa03adf7f956e)
Signed-off-by: Manoj Iyer <manoj.iyer@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>