sdhci-bcm2708: add additional quirks

Some additional quirks are needed for correct operation.
There's no SDHCI capabilities register documented, and it always reads
zero, so add SDHCI_QUIRK_MISSING_CAPS. Apparently
SDHCI_QUIRK_NO_HISPD_BIT is needed for many cards to work correctly in
high-speed mode, so add it as well.