ARM: dts: at91: usb_a9g20: move wrong RTC node

Only the LPW variant has the external RTC. Move it to that board
specific DT. As a result, the common include for A9G20 boards can
go now.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20250402204856.5197-5-wsa+renesas@sang-engineering.com


Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>