The 5.10 target config defined a baseline i686 CPU aligned to the 32-bit
generic subtarget. However, the legacy subtarget arch wasn't set to the
older 586MMX, defaulting instead to the i686.
Explicitly set the subtarget arch and refresh the subtarget config, as done
already with the old geode subtarget.
Fixes: 8391781389 ("x86: support kernel 5.10")
Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
662ceebc4c