Rather than open coding the polling loop in mmc_do_erase(), let's convert
to use mmc_poll_for_busy().

To allow a slightly different error parsing during polling, compared to the
__mmc_switch() case, a new in-parameter to mmc_poll_for_busy() is needed,
but other than that the conversion is straight forward.

Besides addressing the open coding issue, moving to mmc_poll_for_busy() for
erase/trim/discard improves the behaviour according to below.

- Adds support for polling via the optional ->card_busy() host ops.
- Returns zero to indicate success when the final polling attempt finds the
  card non-busy, even if the timeout expired.
- Exits the polling loop when state moves to R1_STATE_TRAN, rather than
  when leaving R1_STATE_PRG.
- Decreases the starting range for throttling to 32-64us.
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Baolin Wang <baolin.wang7@gmail.com>
Tested-by: Ludovic Barre <ludovic.barre@st.com>
Reviewed-by: Ludovic Barre <ludovic.barre@st.com>
Link: https://lore.kernel.org/r/20200204085449.32585-9-ulf.hansson@linaro.org