Add sdk_version to the 'libeign' module

Add the sdk_version to a cc_library_headers module 'libeigen', which is
needed in converting .mk files including this module to a .bp file.
Please check the bug below for more details.

Cherrypicked from I11dc1fc899ce9697fa421c4526527277dcea6aff

Bug: 206089870
Test: rum 'm module-name'
Test: TreeHugger
Change-Id: I11dc1fc899ce9697fa421c4526527277dcea6aff
Merged-In: I11dc1fc899ce9697fa421c4526527277dcea6aff
(cherry picked from commit 4ea03aa63648678de0ee0cab9beb660f6937a612)