mmc: dw_mmc: Only enable CD after setup and only if needed

mmc: dw_mmc: Only enable CD after setup and only if needed

We really don't want to get a card detect interrupt during probe time
since it can confuse things.  Let's disable the card detect interrupt
until we're in a really good place: the end of probe.  Let's also
simply avoid enabling the card detect interrupt if it's not used.

It appears that (at least on rk3288) when vqmmc is turned on it can
cause a bogus "card detect" interrupt.  That meant that we were
getting a predictable card detect interrupt while we were in
mmc_add_host().  On the version of the kernel I'm working with at
least (3.14), this is not a great time to get a card detect interrupt
since I think that we don't grab all the needed locks in
mmc_add_host() and children.  I put stack dumps in dw_mci_setup_bus()
and found that I could see two distinct stack crawls that looked like:

Caller one:
* dw_mci_setup_bus
* dw_mci_set_ios
* mmc_power_up
* mmc_start_host
* mmc_add_host

Caller two:
* dw_mci_setup_bus
* dw_mci_set_ios
* mmc_set_chip_select
* mmc_go_idle
* mmc_rescan
* process_one_work
* worker_thread
* kthread

Signed-off-by: Doug Anderson <dianders@chromium.org>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>