mmc: sdhci: cmdq: add notification for cmdq halt

During halted CMDQ mode, HW expects descriptors sizes
same as used in CMDQ mode.
Our SW uses the legacy path (SDHCI) in case CMDQ is halted,
thus, we need to update legacy path of the fact that we
are in Halted CMDQ state so it can adjust the descriptors
size accordingly.
This change adds a notification mechanism for that purpose.

Change-Id: Iabb473696fb11827dfcce9b137c26b2c5a5a879d
Signed-off-by: Talel Shenhar <tatias@codeaurora.org>