phy: ti: Fix compilation failures without REGMAP

This driver requires regmap or the compile fails:

drivers/phy/ti/phy-gmii-sel.c:43:27: error: array type has incomplete element type ‘struct reg_field’
  const struct reg_field (*regfields)[PHY_GMII_SEL_LAST];

Add it to kconfig.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>