ARM: dts: msm: specify AOP QMP mailbox for gpu_cx_gdsc on SM8150

Specify an AOP QMP mailbox for gpu_cx_gdsc so that an AOP request
is used to enable the GDSC via a special sequence instead of a
direct register write to set SW_COLLAPSE=0.  This is needed to
avoid a NOC error when enabling gpu_cx_gdsc.

Change-Id: I7c2e2edb4e3efc15ba1c98b4a4696015bd878e56
Signed-off-by: David Collins <collinsd@codeaurora.org>