drivers: net: phy: micrel: fix build errors with CONFIG_DM_ETH

drivers: net: phy: micrel: fix build errors with CONFIG_DM_ETH

When Micrel phy is selected without CONFIG_PHY_MICREL_KSZ9031 or
CONFIG_PHY_MICREL_KSZ9021 there  is a build error. Fixing this
by adding proper ifdefs

drivers/net/phy/micrel.c:370:39: error: array type has incomplete element type
 static const struct ksz90x1_reg_field ksz9031_ctl_grp[] =
                                       ^
drivers/net/phy/micrel.c:372:39: error: array type has incomplete element type
 static const struct ksz90x1_reg_field ksz9031_clk_grp[] =
                                       ^
drivers/net/phy/micrel.c: In function ‘ksz9031_of_config’:
drivers/net/phy/micrel.c:377:23: error: array type has incomplete element type
  struct ksz90x1_ofcfg ofcfg[] = {
                       ^
drivers/net/phy/micrel.c:379:13: error: ‘ksz90x1_rxd_grp’ undeclared (first use in this function)
   { MII_KSZ9031_EXT_RGMII_RX_DATA_SKEW, 2, ksz90x1_rxd_grp, 4 },
             ^
drivers/net/phy/micrel.c:379:13: note: each undeclared identifier is reported only once for each function it appears in
drivers/net/phy/micrel.c:380:13: error: ‘ksz90x1_txd_grp’ undeclared (first use in this function)
   { MII_KSZ9031_EXT_RGMII_TX_DATA_SKEW, 2, ksz90x1_txd_grp, 4 },
             ^
drivers/net/phy/micrel.c:386:3: warning: implicit declaration of function ‘ksz90x1_of_config_group’ [-Wimplicit-function-declaration]
   ret = ksz90x1_of_config_group(phydev, &(ofcfg[i]));
   ^
drivers/net/phy/micrel.c:377:23: warning: unused variable ‘ofcfg’ [-Wunused-variable]
  struct ksz90x1_ofcfg ofcfg[] = {
                       ^
drivers/net/phy/micrel.c: At top level:
drivers/net/phy/micrel.c:370:39: warning: ‘ksz9031_ctl_grp’ defined but not used [-Wunused-variable]
 static const struct ksz90x1_reg_field ksz9031_ctl_grp[] =
                                       ^
drivers/net/phy/micrel.c:372:39: warning: ‘ksz9031_clk_grp’ defined but not used [-Wunused-variable]
 static const struct ksz90x1_reg_field ksz9031_clk_grp[] =
                                       ^
scripts/Makefile.build:277: recipe for target 'drivers/net/phy/micrel.o' failed
make[1]: *** [drivers/net/phy/micrel.o] Error 1
Makefile:1201: recipe for target 'drivers/net/phy' failed
make: *** [drivers/net/phy] Error 2
make: *** Waiting for unfinished jobs....

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>