serial: lantiq: Make IRQ & ISR assignment dynamic

This driver/IP is reused across multiple SoCs. Older SoCs supported three
separate IRQs for tx, rx & err interrupts. Newer Lightning Mountain SoC
supports single IRQ for all of tx/rx/err interrupts. This patch modifies
the driver design to support dynamic assignment of IRQ resources & ISRs
based on devicetree node compatible entries.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Rahul Tanwar <rahul.tanwar@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Link: https://lore.kernel.org/r/b166a0593bee191fcd77b5bdf8fedc6f6330a371.1565257887.git.rahul.tanwar@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>