ARM: DRA7: hwmod: Add data for GPTimer 12

Add the hwmod data for GPTimer 12. GPTimer 12 is present in
WKUPAON power domain and is clocked from a secure 32K clock.
GPTimer 12 serves as a secure timer on HS devices, but is
available for kernel on regular GP devices.

The hwmod link is registered only on GP devices. The hwmod data
also reused the existing timer class instead of reintroducing
the identical dra7xx_timer_secure_sysc class which was dropped
in commit edec1786 ("ARM: DRA7: hwmod: Fix the hwmod class
for GPTimer4").

Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>