doc: Add missing html redirect entries for mimxrt10{20,60,64}_evk boards

The mimxrt10{20,60,64}_evk board docs were renamed from <board>.rst to
index.rst in commit 0e4ff809 but were
missing entries in the html redirect list. Add them.

An entry for mimxrt1015_evk is not added because this board always had
an index.rst board doc.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>