feat(plat/rcar3): emit RPC status to DT fragment if RPC unlocked

In case the RCAR_RPC_HYPERFLASH_LOCKED is 0, emit DT node /soc/rpc@ee200000
with property status = "okay" into the DT fragment passed to subsequent
software, to indicate the RPC is unlocked.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Change-Id: Id93c4573ab1c62cf13fa5a803dc5818584a2c13a