acpi: EJ0 method name patching

acpi: EJ0 method name patching

Modify ACPI to only supply _EJ0 methods for PCI slots that support hotplug.

This is done by runtime patching:
- Instrument SSDT ASL code with ACPI_EXTRACT directives
  tagging _EJ0 and _ADR fields.
- At compile time, tools/acpi_extract.py looks for these methods
  in ASL source finds the matching AML, and stores the offsets
  of these methods in tables named aml_ej0_name and aml_adr_dword.
- At run time, go over aml_ej0_name, use aml_adr_dword
  to get slot information and check which slots support hotplug.

  If hotplug is disabled, we patch the _EJ0 NameString in ACPI table,
  replacing _EJ0 with EJ0_.

  Note that this has the same checksum, but is ignored by OSPM.

Note: the method used is robust in that we don't need
to change any offsets manually in case of ASL code changes.
As all parsing is done at compile time, any unexpected input causes
build failure, not a runtime failure.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>