linux: build after intel-microcode if enabled for early loading support

To support building in (a subset of) the intel-microcode files into the
kernel using the CONFIG_EXTRA_FIRMWARE option, we need to ensure that the
microcode files are installed before the Linux kernel is built.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -64,7 +64,8 @@ LINUX_MAKE_ENV = \
 	BR_BINARIES_DIR=$(BINARIES_DIR)
 
 LINUX_INSTALL_IMAGES = YES
-LINUX_DEPENDENCIES = host-kmod
+LINUX_DEPENDENCIES = host-kmod \
+	$(if $(BR2_PACKAGE_INTEL_MICROCODE),intel-microcode)
 
 # Starting with 4.16, the generated kconfig paser code is no longer
 # shipped with the kernel sources, so we need flex and bison, but