ARM: dts: msm: Make allocation for diag as guaranteed on sdm845

Currently, memshare allocates 5MB memory to diag client on
receiving requests from modem. With the patch diag client
will be considered guaranteed on sdm845 to avoid memory
allocation failure on modem SSRs. Marking diag guaranteed
client allocated memory will never be freed.

Change-Id: I97ee7bdeea160e087d9fd5e40b097ea63a4622e4
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>