mmc: renesas_sdhi: use extra flag for CBSY usage

There is one SDHI instance on Gen2 which does not have the CBSY bit.
So, turn CBSY usage into an extra flag and set it accordingly. This has
the additional advantage that we can also set it for other incarnations
later.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Chris Brandt <Chris.Brandt@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>