mmc: core: Respect host's max_busy_timeout when sending sleep cmd

When sending the sleep command for host drivers supporting
MMC_CAP_WAIT_WHILE_BUSY, we need to confirm that max_busy_timeout is
big enough comparing to the sleep timeout specified from card's
EXT_CSD. If this isn't case, we use a R1 response instead of R1B and
fallback to use a delay instead.

Do note that a max_busy_timeout set to zero by the host, is interpreted
as it can cope with whatever timeout the mmc core provides it with.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>