ARM: DRA7: hwmod_data: Add mailbox hwmod data

Add the hwmod data for the 13 instances of the system mailbox
IP in DRA7 SoC. The patch is needed for performing a soft-reset
while configuring the respective mailbox instance, otherwise is
a non-essential change for functionality. The modules are smart
idled on reset, and the IP module mode is hardware controlled.

Cc: Rajendra Nayak <rnayak@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>