hw/sd: ssi-sd: Fix incorrect card response sequence

hw/sd: ssi-sd: Fix incorrect card response sequence

Per the "Physical Layer Specification Version 8.00" chapter 7.5.1,
"Command/Response", there is a minimum 8 clock cycles (Ncr) before
the card response shows up on the data out line. However current
implementation jumps directly to the sending response state after
all 6 bytes command is received, which is a spec violation.

Add a new state PREP_RESP in the ssi-sd state machine to handle it.

Fixes: 775616c3ae8c ("Partial SD card SPI mode support")
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210123104016.17485-4-bmeng.cn@gmail.com>
[PMD: Change VMState version id 2 -> 3]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>