mfd: tps65910: Move interrupt implementation code to mfd file

In place of implementing the irq support in separate file,
moving implementation to main mfd file.
The irq files only contains the table and init steps only
and does not need extra file to have this only for this
purpose.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>