ARM: dts: msm: Make allocation for diag as guaranteed on msm8998

Currently, memshare allocates 5MB memory to diag client on
receiving requests from modem. With the patch diag client
will be considered guaranteed on msm8998 to avoid memory
allocation failure on modem SSRs. Marking diag guaranteed
client allocated memory will never be freed.

Change-Id: I93fa8ae34d2268f6a18c7311b6833ed7e33ab30b
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>