mmc: pwrseq: add support for Marvell SD8787 chip

Allow power sequencing for the Marvell SD8787 Wifi/BT chip.
This can be abstracted to other chipsets if needed in the future.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>