ARM: DRA7: hwmod: Fix the hwmod class for GPTimer4

GPTimer 4 is a regular timer and not a secure timer, so fix
the hwmod to use the correct hwmod class (even though there
are no differences in the class definition itself).

Signed-off-by: Suman Anna <s-anna@ti.com>
[paul@pwsan.com: dropped dra7xx_timer_secure_hwmod_class and
 dra7xx_timer_secure_sysc to avoid compiler warnings]
Signed-off-by: Paul Walmsley <paul@pwsan.com>