fix build on server

Makefile

@@ -2,8 +2,13 @@ obj-m += remoteproc-shm.o
 #dtb-y += rproc-shm.dtb
 KERNEL_SRC ?= $(SDKTARGETSYSROOT)/usr/src/kernel/
 LDFLAGS ?= ""
+TARGETS =
 
-all: $(KERNEL_SRC)/scripts/basic/fixdep $(KERNEL_SRC)/scripts/mod/modpost 
+ifdef SDKTARGETSYSROOT
+TARGETS += $(KERNEL_SRC)/scripts/basic/fixdep $(KERNEL_SRC)/scripts/mod/modpost 
+endif
+
+all: $(TARGETS)
 	make -C $(KERNEL_SRC) M=$(PWD) modules
 
 dtbs: $(dtb-y)
@@ -20,6 +25,7 @@ install:
 
 modules_install:
 	make -C $(KERNEL_SRC) M=$(PWD) modules_install
+
 $(KERNEL_SRC)/scripts/basic/fixdep:
 	cd $(KERNEL_SRC)
 	make -C $(KERNEL_SRC) scripts/basic/