On these several HP laptops, the microphone mute hotkey is "Fn+F8" and
the scancode for this hotkey is 0x81, but this scancode was mapped to
fn_esc in the HP generic keymap section. To fix this problem, we add
a machine specific keymap section to add the correct keymap rule.
BugLink: https://bugs.launchpad.net/bugs/1409721
BugLink: https://bugs.launchpad.net/bugs/1334968
Signed-off-by: Hui Wang <hui.wang@canonical.com>