mmc: Add SPL_MMC_PWRSEQ to fix link issue when building SPL

mmc: Add SPL_MMC_PWRSEQ to fix link issue when building SPL

With MMC_PWRSEQ enabled the following link issue may happen when
building SPL and SPL_PWRSEQ is not enabled.

  aarch64-linux-gnu-ld.bfd: drivers/mmc/meson_gx_mmc.o: in function `meson_mmc_probe':
  drivers/mmc/meson_gx_mmc.c:295: undefined reference to `pwrseq_set_power'

Fix this by adding a SPL_MMC_PWRSEQ Kconfig option used to enable mmc
pwrseq support in SPL.

Also add depends on DM_GPIO to fix following link issue:

  aarch64-linux-gnu-ld.bfd: drivers/mmc/mmc-pwrseq.o: in function `mmc_pwrseq_set_power':
  drivers/mmc/mmc-pwrseq.c:26: undefined reference to `gpio_request_by_name'
  aarch64-linux-gnu-ld.bfd: drivers/mmc/mmc-pwrseq.c:29: undefined reference to `dm_gpio_set_value'
  aarch64-linux-gnu-ld.bfd: drivers/mmc/mmc-pwrseq.c:31: undefined reference to `dm_gpio_set_value'

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Ferass El Hafidi <vitali64pmemail@protonmail.com>