net: airoha: Fix typos in comments and Kconfig

net: airoha: Fix typos in comments and Kconfig

Fix several typos found during code review:
- Kconfig: "Aiorha" -> "Airoha" in NET_AIROHA_FLOW_STATS help text
- Comment: "CMD1" -> "CDM1" (Central DMA, not Command)
- Comments: "GMD1/2/3/4" -> "GDM1/2/3/4" (Gigabit DMA, not GMD)

These are pure comment and documentation fixes with no functional impact.

Signed-off-by: Wayen.Yan <win847@gmail.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/6a2ca74a.c5b1db4e.21a698.01e7@mx.google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>