common: miiphyutil: Work and report phy address in hex in mdio cmd

It is confusing that mdio commands work and report phy id as
decimal value when mii is working with hex values.

For example:
ZynqMP> mdio list
gem:
21 - TI DP83867 <--> ethernet@ff0e0000
ZynqMP> mdio read ethernet@ff0e0000 0
Reading from bus gem
PHY at address 21:
0 - 0x1140
ZynqMP> mii dump 21 0
Incorrect PHY address. Range should be 0-31
...
ZynqMP> mii dump 15
0.     (1140)                 -- PHY control register --
  (8000:0000) 0.15    =     0    reset

U-Boot normally takes hex values that's why this patch is changing mdio
command to handle hex instead of changing mii command to handle decimal
values.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>