PCI hotplug: clean up acpi_run_hpp()

This patch cleans up acpi_run_hpp() and follows the style of acpi_run_hpx():
    - remove unnecessary METHOD_NAME__HPP #define
    - use ACPI_ALLOCATE_BUFFER rather than evaluating _HPP twice
    - validate _HPP package length (defined as 4 by the spec)
    - avoid ref to undefined data if FW provides < 4 elements
    - remove temporary nui[] array

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Reviewed-by: Alex Chiang <achiang@hp.com>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Acked-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>