gpio: dwapb: Add debounce reference clock support

gpio: dwapb: Add debounce reference clock support

Aside from the APB reference clock DW GPIO controller can have a
dedicated clock connected to setup a debounce time interval for
GPIO-based IRQs. Since this functionality is optional the corresponding
clock source is also optional. Due to this lets handle the debounce
clock in the same way as it has been developed for the APB reference
clock, but using the bulk request/enable-disable methods.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20200323195401.30338-6-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>