mfd: lpc_sch: Partially revert "Add support for Intel Quark X1000"

The IRQ support for SCH GPIO is not specific to the Intel Quark SoC.
Moreover the IRQ routing is quite interesting there, so while it's
needs a special support, the driver haven't it anyway yet.

Due to above remove basically redundant code of IRQ support.

This reverts commit ec689a8a.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>