soc: stm32: fix rtt on stm32u5 series by enabling GPDMA1 clock

On some STM32 MCUs SEGGER RTT is only working with realtime updates
when DMA is clocked. The STM32U5 series uses a new DMA controller
module called GPDMA.

Refs: #34324
Fixes: #54316

Signed-off-by: Almin Iriskic <almin.iriskic@student.tugraz.at>