i18n.consoleKeyMap: Accept string or path.

i18n.consoleKeyMap maps to KEYMAP=... in vconsole.conf and `loadkeymap'
in stage1. Both of these accept paths to a keymap file in addition to
a string containing the name of the keymap.

With this commit, it's possible to use your own keymap via:

```i18n.consoleKeyMap = ./path/to/something.kmap```

which will be used in stage1 and all virtual terminals.