Declare context for emmc

Declare context for emmc and give permission for RIDL/LogKit. RIDL needs to
be able to write to sysfs dload to enable emmc crashdumps. It also needs to
be able to read/write to the rawdump device block to copy the crashdump for
post processing and mark it as read.

Change-Id: I20d29049e1f382e2e1ef72e812f736edef29a910
CRs-Fixed: 1002379