Port Emulator keymaps.

Also added a validation tool for keymaps (not currently integrated
into the build system but getting there).

This change brings back Android.mk with the intent that it will
be used to validate keymaps in a later change.

Added some missing keys that are present on phones.

Bug: 3215210
Bug: 3225421
Change-Id: Id817c6e2215164616942c51a42752915d9ceacd3