asdk-repo-libdce

libdce[Linux]: Add mutex protection for dce_buf_lock/dce_buf_unlock

The dce_buf_lock and dce_buf_unlock are meant for any video
buffer locking and unlocking with the GEM allocator.
Currently, these methods are being called from libdce apis
with ipc mutex held. In order to enable other media components
to make use of these buffer lock/unlock apis, explicit ipc mutex
protection is added.

Change-Id: Ibb4976120e5dfe6f88b42359655a460cafc223ac
Signed-off-by: Sunita Nadampalli <sunitan@ti.com>