mfd: wcd9xxx: Refactor codec core driver and irq driver

IRQ driver can be used by codecs that do not use the core driver.
Refactor the drivers so that codec drivers that are not children
of the core driver can also request/access the interrupt routines
provided by the IRQ driver.

Change-Id: I3086be02839fd735db2d32665abf7b984958dc2b
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>
(cherry picked from commit c68ed369921e8d08f4254b9243872785a3a5cf2f)
Signed-off-by: Dan Trifan <jimsth@gmail.com>