drivers: pinctrl: Check whether irq mapping exists before creating it

Calling to create mapping without checking if mapping already exists
leads to loop to all available domains to get the corresponding
domain and then checks for available mapping. Client driver calling
gpio_to_irq from atomic context may get sleeping function called from
invalid context.

Add a check to see if irq mapping exist before creating it.

Change-Id: If922b06448138107d5c797f35d2835b20a490ada
Signed-off-by: Raghavendra Kakarla <rkakarla@codeaurora.org>