ARM: dts: marzen: Name serial port pfc subnodes after device names

Name the Pin Function Controller subnodes for SCIF2 and SCIF4 after
their device names, instead of using some arbitrary names that look like
serial port aliases, but differ from the actual aliases.

This avoids conflicts when enabling support for more serial ports later,
either here or in a DT overlay.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>