mmc: sdhci: Improve register dump print format

Ensure all prints start with the mmc host name, and the text all lines up.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Ludovic Desroches <ludovic.desroches@microchip.com>