MSCC: delete obsolete reference to MSCC_BITBANG_SPI_GPIO

Remove "select MSCC_BITBANG_SPI_GPIO" since Kbuild option was deleted
back in commit ace9c103df2875d2b435dbd7b36618020edfd1c0:

  commit ace9c103df2875d2b435dbd7b36618020edfd1c0
  Author: Lars Povlsen <lars.povlsen@microchip.com>
  Date:   Tue Jan 8 10:38:35 2019 +0100

    mips: gpio: mscc: Obsoleted gpio-mscc-bitbang-spi.c
1 file changed