keymap: add extra Alt Gr mapping for Brazillian Portuguese ABNT2 keyboards

[alfredo]

Summary

This adds missing Alt Gr mappings for the keys "q", "w", "e" an "c" to conform with ABNT2 standard [1]

PR: 256416
Submitted by: Neebz <[e-mail]>
MFC after: 2 weeks

[1] http://kbdlayout.info/KBDBR/

Test Plan

test output using an ABNT/ABNT2 keyboard (Brazillian Portuguese) on the following USB-wireless keyboards :

• Microsoft Wireless Keyboard 3000 v2.0

-Dell WK636t

And the following Laptop:

• Microboard Ultimate U342

[emaste]

As I mentioned in the PR I am not familiar with Brazilian keyboards, but the patch looks fine.