Input: add input event to APM event bridge

This patch adds a very simple input power event to APM user suspend
event bridge. Its currently only works for the systems using the
emulated APM driver but could easily be extended to work with anything
with a true APM BIOS too.

This covers a standard embedded system need which is to suspend when the
user presses a suspend button. It leaves options open to system
integrators to ignore (or unload) this code and implement their own more
complex event handling system.

Its hidden behind the EMBEDDED Kconfig option since its only likely to
be of use to embedded style systems. It can be built as a module so the
"hardcoded" policy can easily be removed from the kernel at runtime if
desired too.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>