sdmmc: introduce is_app_cmd flag, check it along with opcode

sdmmc: introduce is_app_cmd flag, check it along with opcode

‘make_hw_cmd’ function checks opcodes in a few cases. Comparing opcode
does not tell the whole story, because for some SD commands there is are
APP commands with the same opcodes. This change introduces a flag which
indicates whether the next command is going to be an APP command.
The check for APP_SET_BUS_WIDTH command is updated to use this flag.
This fixes a bug with an unexpected STOP_TRANSMISSION command sent after
SWITCH_FUNC command, which has opcode 6, same as APP_SET_BUS_WIDTH.