davinci: enbw_cmc: change switch init behaviour

change the behaviour of switch initialization:

- rename "pwl" to "lan" in hwconfig parameter
  "lan" = port 1 with phy addr 2
  "lmn" = port 2 with phy addr 3

- if we have a valid switch config file in flash, do not
  evaluate the settings in the hwconfig "lan" or "lmn"
  subcommand.

- if we have no valid switch config file in flash, start
  the switch with default values, if we have a "lan" or
  a "lmn" hwconfig subcommand. If no "lan" or "lmn" is
  found in hwconfig, do nothing with the switch.

Signed-off-by: Heiko Schocher <hs@denx.de>