mmc: dw_mmc: setpower on MMC_POWER_{UP,OFF}

Call the setpower platform callback in response to set_ios with
ios->power_mode == MMC_POWER_UP or MMC_POWER_OFF, instead of from the
card detect work function.

This appears to fix a problem I have where a card stuck in a funny state
doesn't get properly cleared by the power being turned off, presumably
due to lack of power sequencing. This resulted in the following log
messages after boot:

mmc0: error -110 whilst initialising SD card
mmc_host mmc0: Bus speed (slot 0) = 99840000Hz (slot req 300000Hz, actual 298922HZ div = 167)
mmc0: error -110 whilst initialising SD card
mmc_host mmc0: Bus speed (slot 0) = 99840000Hz (slot req 200000Hz, actual 199680HZ div = 250)
mmc0: error -110 whilst initialising SD card
mmc_host mmc0: Bus speed (slot 0) = 99840000Hz (slot req 195765Hz, actual 195764HZ div = 255)
mmc0: error -110 whilst initialising SD card
mmc_host mmc0: Bus speed (slot 0) = 99840000Hz (slot req 400000Hz, actual 399360HZ div = 125)
mmc0: error -110 whilst initialising SD card
mmc_host mmc0: Bus speed (slot 0) = 99840000Hz (slot req 300000Hz, actual 298922HZ div = 167)

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Seungwon Jeon <tgih.jun@samsung.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>