linux-imx

ahci: imx: add the bist mode sysfile callback for imx8qm sata

In order to do SATA compliance tests, add the bist mode
sysfile callback to generate kinds of test patterns.
- Add the "ahci-imx.bist=1" into kernel command line to
register the bist mode enable callback.
- Use "echo <pattern_#> /sys/devices/.../ahci_bist_pattern"
to generate the responding test pattern.
- Use "cat /sys/devices/.../ahci_bist_pattern" to check
the current pattern configuration.
NOTE:
LBP 0, LFTP 1, MFTP 2, HFTP 3.
- Adjust the TX-DEEMP and COMINT to pass the compliance tests.

BuildInfo:
- SCFW 685bd659, SECO-FW 00000000, IMX-MKIMAGE 53974947, ATF 625d9ed
- U-Boot 2017.03-01018-g6045484

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Frank Li <frank.li@nxp.com>