ARM: dts: msm: Enable memory allocation for diag client for 8920

The new diag client requires additional memory from hlos. This
patch caters to diag memory requirement.

CRs-Fixed: 1082450
Change-Id: Icde1959982ad83d202d8d19683f26e0d989b88c0
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>