ACPI: ibm-acpi: allow module to load when acpi notifiers can't be set (v2)

This patch allows for ibm-acpi to coexist (with diminished functionality) with
other drivers like ACPI_BAY.  ibm-acpi will simply disable the functions it is
not able to register ACPI notifiers for.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Chris Wedgwood <cw@f00f.org>
Cc: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>