net: ethernet: stmmac: remove select QCOM_SOCINFO and make it optional

QCOM_SOCINFO depends on QCOM_SMEM but is not selected, this cause some
problems with QCOM_SOCINFO getting selected with the dependency of
QCOM_SMEM not met.
To fix this remove the select in Kconfig and add additional info in the
DWMAC_IPQ806X config description.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 9ec092d2

 ("net: ethernet: stmmac: add missing sgmii configure for ipq806x")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>