ARM: dts: msm: modify memory reservation requirements for tmc-etr on 8974

The CoreSight TMC-ETR driver is modified to meet its coherent memory
allocation requirement using dma_alloc_coherent api instead of custom
allocate_contiguous_ebi function. Add support to the device tree to
specify this memory requirement.

Also retain the dt entry to allocate contiguous memory via
allocate_contiguous_ebi api until the corresponding driver changes go
in to prevent breaking TMC-ETR functionality.

Change-Id: I67b4813ab45d520311765500513ea265fb33188e
Signed-off-by: Aparna Das <adas@codeaurora.org>