soc/intel/adl/acpi: add FSPI to DSDT

A previous CL ("Add missing ACPI device path names",
commit d22500f0c61f8c8e10d8f4a24e3e2bf031163c07) caused some errors
from the Kernel on Brya devices (see Tim's comment on patchset 8):
> ACPI Error: AE_NOT_FOUND, While resolving a named reference
> package element - \_SB_.PCI0.FSPI

FSPI is defined in src/soc/intel/alderlake/chipset.cb:
device pci 1f.5 alias fast_spi on end

This CL adds the corresponding FSPI device to the DSDT to prevent
the error mentioned above.

TEST=Built and tested on brya by verifying the error is gone.
BUG=b:231582182

Change-Id: I11e89ad2a5d47f6b579f755b0a41399ee3cb856c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69920
Reviewed-by: Tarun Tuli <taruntuli@google.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/alderlake/acpi/serialio.asl

@@ -50,6 +50,12 @@ Device (I2C7)
 	Name (_DDN, "Serial IO I2C Controller 7")
 }
 
+Device (FSPI)
+{
+	Name (_ADR, 0x001f0005)
+	Name (_DDN, "Fast SPI")
+}
+
 Device (SPI0)
 {
 	Name (_ADR, 0x001e0002)