firmware_class: Allow private data in [unmap|map]_fw_mem

Some callers of request_firmware_direct may need additional
context to be able to map firmware memory. Allow private data
to be passed in with request_firmware_direct, and send this
data along with the [unmap|map]_fw_mem callbacks.

Change-Id: I05a15eb46cc663a4476b784e30e80182a28e10c3
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>