Documentation: Support QCA8337 RGMII port0 in sdxprairie

Add support for QCA8337 RGMII port0 in sdxprairie.

Change-Id: I9fb3613098512b9e89d82929f5044216f1b58477
Acked-by: Rahul Kawadgave <rahulak@qti.qualcomm.com>
Signed-off-by: crao <crao@codeaurora.org>
Signed-off-by: Sunil Paidimarri <hisunil@codeaurora.org>