da850/omap-l138: davinci_emac: Suppress auto negotiation if needed

da850/omap-l138: davinci_emac: Suppress auto negotiation if needed

negotiation is enabled in RMII mode. Some boards based on da850 need
to suppress this procedure.

CC: Rajashekhara, Sudhakar <sudhakar.raj@ti.com>
CC: Lad, Prabhakar <prabhakar.lad@ti.com>
CC: Hadli, Manjunath <manjunath.hadli@ti.com>
CC: sbabic@denx.de
Acked-by: Stefano Babic <sbabic@denx.de>
CC: Tom Rini <trini@ti.com>
Signed-off-by: Bastian Ruppert <Bastian.Ruppert@Sewerin.de>
Acked-by: Prabhakar Lad <prabhakar.lad@ti.com>