pmem: remove support for unstable PMEM devices

This functionality has never been used, is ugly and
complicates the DMM design.

Signed-off-by: Larry Bassel <lbassel@codeaurora.org>

include/linux/android_pmem.h

@@ -151,8 +151,6 @@ struct android_pmem_platform_data
 	unsigned cached;
 	/* The MSM7k has bits to enable a write buffer in the bus controller*/
 	unsigned buffered;
-	/* This PMEM is on memory that may be powered off */
-	unsigned unstable;
 	/* which memory type (i.e. SMI, EBI1) this PMEM device is backed by */
 	unsigned memory_type;
 };