The space between 2K and 16K in /misc is currently reserved for vendor's
use (as claimed in bootloader_message.h), but we don't allow vendor
module to access misc_block_device other than vendor_init.
The change in the topic adds a `misc_writer` tool as a vendor module,
which allows writing data to the vendor space to bridge the gap in the
short term. This CL adds matching labels to grant access.
Long term goal is to move /misc as vendor owned, then to provide HAL
access from core domain (b/132906936).
Bug: 132906936
Test: Build crosshatch that includes misc_writer module. Invoke
/vendor/bin/misc_writer to write data to /misc.
Change-Id: I4c18d78171a839ae5497b3a61800193ef9e51b3b
