vc/google/chromeec/acpi: write OIPG in DECLARE_NO_CROS_GPIOS case

When a mainboard selects ACPI_SOC_NVS and CHROMEOS, CHROMEOS_NVS will be
selected. This causes vc/google/chromeec/acpi/chromeos.asl to be
included in the DSDT and chromeos_acpi_gpio_generate to be called when
generating the coreboot SSDT. When a mainboard also uses
DECLARE_NO_CROS_GPIOS(), this will cause variant_cros_gpio.count to be 0
and variant_cros_gpio.gpios to be NULL. chromeos_acpi_gpio_generate only
checked if the GPIO table was non-NULL, which caused the function to
exit early and not generate the OIPG package which causes the kernel to
complain about referencing the non-existing OIPG package. To avoid this,
only exit in the GPIO table pointer being NULL case if the number of
GPIOs is non-0.

TEST=Error about missing OIPG ACPI object in dmesg disappears on birman.

Before:

[    0.241339] chromeos_acpi: registering CHSW 0
[    0.241468] ACPI BIOS Error (bug): Could not resolve symbol [\CRHW.GPIO.OIPG], AE_NOT_FOUND (20220331/psargs-330)
[    0.241703] ACPI Error: Aborting method \CRHW.GPIO due to previous error (AE_NOT_FOUND) (20220331/psparse-531)
[    0.241933] chromeos_acpi: failed to retrieve GPIO (5)
[    0.242011] chromeos_acpi: registering VBNV 0
[    0.242113] chromeos_acpi: registering VBNV 1
[    0.242284] chromeos_acpi: truncating buffer from 3072 to 1336
[    0.242462] chromeos_acpi: installed

With the patch applied:

[    0.242580] chromeos_acpi: registering CHSW 0
[    0.242714] chromeos_acpi: registering VBNV 0
[    0.242817] chromeos_acpi: registering VBNV 1
[    0.242990] chromeos_acpi: truncating buffer from 3072 to 1336
[    0.243249] chromeos_acpi: installed

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: Fred Reitberger <reitbergerfred@gmail.com>
Change-Id: Ie340003afb718b1454c2da4a479882b71714c3c7
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74375
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/vendorcode/google/chromeos/acpi.c b/src/vendorcode/google/chromeos/acpi.c
index 801f33d..fb6d0a5 100644
--- a/src/vendorcode/google/chromeos/acpi.c
+++ b/src/vendorcode/google/chromeos/acpi.c
@@ -14,7 +14,7 @@
 
 	num = variant_cros_gpio.count;
 	gpios = variant_cros_gpio.gpios;
-	if (!gpios)
+	if (num && !gpios)
 		return;
 
 	acpigen_write_scope("\\");