mailbox/omap: use of_device_get_match_data() to get match data

The OMAP Mailbox driver is directly using an integer value as
match data for distinguishing the interrupt register layout
between OMAP2 and OMAP4+ SoCs. Introduce a dedicated structure
for storing this match data, and simplify the probe function by
using the of_device_get_match_data() function. This allows the
driver to scale for 64-bit platforms by eliminating the unnecessary
type-casting between a u32 and a void pointer types.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>