linux: Make dtc install step more reliable

Checking for the existence of the dtc binary built by the
non-dependent dtc package may cause instable behaviour when giving more
freedom on the order of how the packages are built (parallelization).

In addidion, when moving to per-package host/target method, the check
would always trigger in the isolated host, leading to linux-dtc always
being installed as dtc.
This in turn may lead to undesired overwriting of the real host-dtc binary
when finally assembling the global host dir.

Thus rework the linux-dtc install condition to be defined by configuration
rather than compile time order.

Signed-off-by: Andreas Naumann <anaumann@ultratronik.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 860906ee05fad3fe503786ec7c656ea0f25851fc)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -446,9 +446,7 @@ define LINUX_INSTALL_HOST_TOOLS
 	# Installing dtc (device tree compiler) as host tool, if selected
 	if grep -q "CONFIG_DTC=y" $(@D)/.config; then \
 		$(INSTALL) -D -m 0755 $(@D)/scripts/dtc/dtc $(HOST_DIR)/bin/linux-dtc ; \
-		if [ ! -e $(HOST_DIR)/bin/dtc ]; then \
-			ln -sf linux-dtc $(HOST_DIR)/bin/dtc ; \
-		fi \
+		$(if $(BR2_PACKAGE_HOST_DTC),,ln -sf linux-dtc $(HOST_DIR)/bin/dtc;) \
 	fi
 endef