char: virtio_fastrpc: Add virtio frontend fastrpc driver

This driver provides the same interface for fastrpc library as metal Linux.
So fastrpc applications and library can run in GVM without modification.

Change-Id: I0ec9a6d0afaa41c6e88961b471ecd8281a2989a7
Signed-off-by: Ping Jiang <scottjiang@codeaurora.org>