drivers: qcom: cmd-db: add Command DB driver

Command DB is a dynamic device database available in the shared memory.
The database houses the addresses and configuration information of the
hardened resource blocks. QTI drivers may query this database to find
the dynamic address of their resource for this SoC and send state
requests to those resources.

This is a snapshot as of 'commit b4a69c05b01172 ("drivers: mailbox:
rpmh-mailbox: rename file to match convention")'.

Change-Id: Iec7cc64146c5c2e214321b47d9068bae745034c9
Signed-off-by: Lina Iyer <ilina@codeaurora.org>