Stop assuming that pvmfw.img can only be pre-built

Introduce the BOARD_USES_PVMFWIMAGE variable, similarly to all other
partitions, and use it where appropriate (in particular, where the
soon-to-be incorrect assumption that pvmfw.img could only be a pre-built
board image was made).

Bug: 199717422
Test: m ${ANDROID_PRODUCT_OUT}/pvmfw.img # with TARGET_PKVM_ENABLED=true
Change-Id: I8f4faa78c741d29b473303b521834387dbd48cd1
diff --git a/core/board_config.mk b/core/board_config.mk
index 53dbb92..56c3e71 100644
--- a/core/board_config.mk
+++ b/core/board_config.mk
@@ -695,6 +695,12 @@
 endif
 .KATI_READONLY := BUILDING_ODM_DLKM_IMAGE
 
+BOARD_USES_PVMFWIMAGE :=
+ifdef BOARD_PREBUILT_PVMFWIMAGE
+  BOARD_USES_PVMFWIMAGE := true
+endif
+.KATI_READONLY := BOARD_USES_PVMFWIMAGE
+
 ###########################################
 # Ensure consistency among TARGET_RECOVERY_UPDATER_LIBS, AB_OTA_UPDATER, and PRODUCT_OTA_FORCE_NON_AB_PACKAGE.
 TARGET_RECOVERY_UPDATER_LIBS ?=