soc: stm32l0: enable DMA clock to fix Hardfault linked to DBGMCU bits

On STM32L0, there are some hardfault when DBGMCU bit Sleep, Stop
or Standby are enabled. See #37119
For unclear reason, enabling DMA clock fixes this issue.
(similarly than #38561, DMA clock comes with DBGMCU bits)

Signed-off-by: Alexandre Bourdiol <alexandre.bourdiol@st.com>