arm64: dts: realtek: rtd129x: Use reserved-memory for RPC regions

Move /reserved-memory node from RTD1295 to RTD129x DT.
Convert RPC /memreserve/s into /reserved-memory nodes.

Fixes: 72a7786c ("ARM64: dts: Add Realtek RTD1295 and Zidoo X9S")
Fixes: f8b3436d ("arm64: dts: realtek: Factor out common RTD129x parts")
Signed-off-by: Andreas Färber <afaerber@suse.de>