mmc: core: Rework cd-gpio handling

There are a few places around the code that invert inverted and possibly
inverted CD line. That's really confusing. Squash them all into one place
in mmc_gpiod_request_cd(). MMC_CAP2_CD_ACTIVE_HIGH is used analogously to
WP line: in GPIO mode it is used only at probe time to switch polarity, for
native mode it is left as is.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Link: https://lore.kernel.org/r/db189b715596d63caf8c6a088bddc71dd69a879b.1576031637.git.mirq-linux@rere.qmqm.pl


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>