ANDROID: GKI: bring back irq_create_mapping()

Upstream commit bb4c6910c8b4 ("genirq/irqdomain: Add an
irq_create_mapping_affinity() function") ended up removing the
irq_create_mapping() function and replacing it with an inline function.
That's fine, except that this function was one of our "must support" api
calls, so put it back as an exported function to preserve the ABI.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ibb1c480c0ba4eb8b3d6c71cabf83467ee2d1f12b