ARM: dts: msm: Modify memory allocation for diag on sdm845

The patch removes the boot time allocation for diag and allocates
only on request from peripheral. The new property added ensures
memory will not be freed on free request or ssr case.

Change-Id: I18882de4ce93ec52772553d67789ed89789f5b40
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>