gpu: drm: bridge: improve the function of getting training status

When reading link status, the request size is 13, but this real return
size from ls1028 dp firmware is 10, they don't match with each other.
So, getting training status operation is failed, and cause the whole
display driver initializes failed. This issue is introduced by commit
7ce8d36a

("MLK-25748: gpu: drm: bridge: Added support for
fast link training"). But the root cause is that the dp firmware of
ls1028 platform from the latest LSDK2108 does not support the fast
link training. Because NXP never upgrade the ls1028 dp firmware since
LSDK2004, it still sends 10 bytes to mhdp driver, and then cause parse
command failed. This issue also occurs since LSDK2012.
In order to work with the current dp firmware of ls1028 platform and
not affect imx series platforms, so create a special case to process
ls1028 platform.

Signed-off-by: Meng Li <Meng.Li@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>