u-boot.mk: fix pkg-config usage

Using Host/Exports doesn't work as intended, explicitly add the
required vars so that u-boot finds the required libraries when building
its tools.

Signed-off-by: Andre Heider <a.heider@gmail.com>

include/u-boot.mk

@@ -45,6 +45,9 @@ UBOOT_MAKE_FLAGS = \
 	HOSTCC="$(HOSTCC)" \
 	HOSTCFLAGS="$(HOST_CFLAGS) $(HOST_CPPFLAGS) -std=gnu11" \
 	HOSTLDFLAGS="$(HOST_LDFLAGS)" \
+	STAGING_PREFIX="$(STAGING_DIR_HOST)" \
+	PKG_CONFIG_PATH="$(STAGING_DIR_HOST)/lib/pkgconfig" \
+	PKG_CONFIG_LIBDIR="$(STAGING_DIR_HOST)/lib/pkgconfig" \
 	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='')
 
 define Build/U-Boot/Target

package/boot/uboot-mediatek/Makefile

@@ -111,8 +111,6 @@ UBOOT_TARGETS := \
 
 UBOOT_MAKE_FLAGS += $(UBOOT_IMAGE:.fip=.bin)
 
-Build/Exports:=$(Host/Exports)
-
 define Build/fip-image
 	$(STAGING_DIR_HOST)/bin/fiptool create \
 		--soc-fw $(STAGING_DIR_IMAGE)/$(BUILD_SUBTARGET)-$(BL2_BOOTDEV)-$(BL2_DDRBLOB)ddr-bl31.bin \

package/boot/uboot-mvebu/Makefile

@@ -53,8 +53,6 @@ UBOOT_TARGETS:= \
 	espressobin \
 	uDPU
 
-Build/Exports:=$(Host/Exports)
-
 define Build/Configure
 	# enable additional options beyond <device>_defconfig
 	echo CONFIG_CMD_SETEXPR=y >> $(PKG_BUILD_DIR)/configs/$(UBOOT_CONFIG)_defconfig

package/boot/uboot-mxs/Makefile

@@ -38,8 +38,6 @@ UBOOT_TARGETS := \
 
 UBOOT_MAKE_FLAGS += $(UBOOT_IMAGE)
 
-Build/Exports:=$(Host/Exports)
-
 define Build/InstallDev
 	$(INSTALL_DIR) $(STAGING_DIR_IMAGE)
 	$(INSTALL_BIN) $(PKG_BUILD_DIR)/$(UBOOT_IMAGE) $(STAGING_DIR_IMAGE)/$(BUILD_VARIANT)-$(UBOOT_IMAGE)

package/boot/uboot-zynq/Makefile

@@ -60,6 +60,4 @@ endef
 define Package/u-boot/install/default
 endef
 
-Build/Exports:=$(Host/Exports)
-
 $(eval $(call BuildPackage/U-Boot))