ARM: dts: imx25/27-eukrea: Fix RTC node name

[ Upstream commit 68c711b882c262e36895547cddea2c2d56ce611d ]

Node names should be generic. Use 'rtc' as node name to fix
the following dt-schema warning:

imx25-eukrea-mbimxsd25-baseboard.dtb: pcf8563@51: $nodename:0: 'pcf8563@51' does not match '^rtc(@.*|-([0-9]|[1-9][0-9]+))?$'
	from schema $id: http://devicetree.org/schemas/rtc/nxp,pcf8563.yaml#



Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>