target: add symbols for i386/x86_64 cpu features

Selecting the target subarchitecture variant automatically selects the
appropriated set of features.

[thomas.petazzoni@free-electrons.com:
  removed depends on inside hidden options, not needed.
  removed SSE41/SSE42 options, not used.]

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>