target-tricore: Make TRICORE_FEATURES implying others.

Since all the TriCore instructionsets are subsets of each other (1.3 C 1.3.1 C 1.6),
make the features implying each other, e.g 1.6 also has 1.3.1 and 1.3. This way
we only need to check our features for the instructionset, where a instruction was first introduced.

Signed-off-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Reviewed-by: Richard Henderson <rth@twiddle.net>
