mmc: sdhci: move sdhci_reset() call to sdhci_init()

If CONFIG_BLK is enabled, add_sdhci() is never called.
So, sdhci_reset() is not called, either.  This is a problem for
my board as it needs the reset to start from a sane state.

Move the add_sdhci() call to sdhci_init(), which is visited
by both of the with/without CONFIG_BLK cases.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>