ipmi: acpi: use relative path to resource source

ipmi: acpi: use relative path to resource source

smbus-ipmi AML description needs to specify a path to its parent
node in _CRS. The rest of IPMI inplementations (ISA based)
do not need path at all. Instead of passing through a full path
use relative path to point to smbus-ipmi's parent node, it will
let follow up patches to create IPMI device AML in a generic
way instead of current ad-hoc way. (i.e. AML will be generated
the same way it's done for other ISA device, and smbus will be
converted to generate AML for its slave devices the same way
as ISA)

expected AML change:
     Name (_CRS, ResourceTemplate ()  // _CRS: Current Resource Settings
     {
        I2cSerialBusV2 (0x0000, ControllerInitiated, 0x000186A0,
-           AddressingMode7Bit, "\\_SB.PCI0.SMB0",
+           AddressingMode7Bit, "^",
            0x00, ResourceProducer, , Exclusive,
            )
      })

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20220608135340.3304695-14-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>