drivers: ethernet: eth_stm32_hal: Add stm32n6 ethernet support

-Update the ETH_STM32_HAL menu configuration to conditionally
 select USE_STM32_HAL_RIF if SOC_SERIES_STM32N6X is enabled.

-Align Ethernet descriptors to 32 bytes for STM32N6 to ensure
 efficient DMA operations and improve cache line efficiency
 and overall performance

-Add RISAF configuration in eth_initialize function for STM32N6
 series to set up master and slave security attributes
 for the Ethernet peripheral.

-Ensure RISAF configuration is done before enabling
 the Ethernet clock to maintain proper security attributes.

Signed-off-by: IBEN EL HADJ MESSAOUD Marwa <marwa.ibenelhadjmessaoud-ext@st.com>