drivers: ethernet: enable TC375 GETH RMII path

[ruka77S]

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Description
This series enables the TC375 Lite Kit GETH RMII path under Zephyr.

Changes:

• Enable TC3x STM clock before system timer register access.
• Configure the AURIX GETH wrapper clock, KRST, and RMII GPCTL path.
• Apply eth0 pinctrl in the DWC EQoS MAC driver.
• Fix DWC EQoS DMA interrupt channel-bit clearing.
• Fix an RX stats iface typo.
• Correct DP83825 RMII RCSR reference clock selection.

Validated on KIT_A2G_TC375_LITE:

• Serial output reaches the eth_test main loop.
• DP83825 reports 100 Mbps full duplex link.
• Board IPv4: 192.168.1.10/24.
• PC ping succeeds with:
  ping -S 192.168.1.20 192.168.1.10

Related Issue
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Context
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