irqchip: Conexant CX92755 interrupts controller driver

Add interrupt controller driver to the Conexant CX92755 SoC, part of the
Digicolor SoCs series. Use the generic irq framework support. Use syscon to
access the system global UC_IRQ_CONTROL register.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/5b769e3c23dfa5fde08c4f3bc966c2c2b3921d8a.1421317616.git.baruch@tkos.co.il
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>