Hvmloader: Modify ACPI to only supply _EJ0 methods for PCIslots that support hotplug by runtime patching

In Xen platform, after using upstream qemu, the all of pci devices will show
hotplug in the windows guest. In this situation, the windows guest may occur
blue screen when VM' user click the icon of VGA card for trying unplug VGA card.
However, we don't hope VM's user can do such dangerous operation, and showing
all pci devices inside the guest OS is unfriendly.

This is done by runtime patching:
  - Rename _EJ0 methods for PCI slots in DSDT to EJ0_:note that this has the
    same checksum, but is ignored by OSPM.
  - At compile time, look for these methods in ASL source,find the matching AML,
    and store the offsets of these methods in a table named aml_ej0_data.
  - At run time, go over aml_ej0_data, check which slots not support hotplug and
    patch the ACPI table, replacing _EJ0 with EJ0_.

Signed-off-by: Gaowei <gao.gaowei@huawei.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>