mmc: dw_mmc: add voltage switch command flag

mmc: dw_mmc: add voltage switch command flag

During a voltage switch command (CMD11, opcode: SD_CMD_SWITCH_UHS18V),
certain hosts tend to stop responding to subsequent commands. This is
addressed by introducing an additional command flag,
DWMCI_CMD_VOLT_SWITCH.

The associated interrupt bit is defined as DWMCI_INTMSK_VOLTSW. This is
set high when a voltage switch is issued, this needs to be waited for
and set to low. Implement the same in the timeout loop. Do note that
since DWMCI_INTMSK_VOLTSW shares the same bit as DWMCI_INTMSK_HTO (bit
10), the interrupt bit needs to be polled for only if the volt switch
command is issued.

DWMCI_CMD_VOLT_SWITCH also needs to be set for subsequent clken commands
after the volt switch. To ensure this, add a boolean member in the host
private struct (herein named volt_switching), which informs if the last
command issued was for volt switching or not.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>