build: use new toolchain variables for tools

This change migrates the values of `CC`, `CPP`, `AS` and other toolchain
variables to the new `$(toolchain)-$(tool)` variables, which were
introduced by the toolchain refactor patch. These variables should be
equivalent to the values that they're replacing.

Change-Id: I644fe4ce82ef1894bed129ddb4b6ab94fb04985d
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/tools/marvell/doimage/Makefile b/tools/marvell/doimage/Makefile
index 0766f59..6e59aa2 100644
--- a/tools/marvell/doimage/Makefile
+++ b/tools/marvell/doimage/Makefile
@@ -29,7 +29,6 @@
 # could get pulled in from firmware tree.
 INCLUDE_PATHS = -I.
 
-HOSTCC ?= gcc
 RM := rm -rf
 
 .PHONY: all clean
@@ -38,14 +37,14 @@
 
 ${PROJECT}: ${OBJECTS} Makefile
 	@echo "  HOSTLD  $@"
-	${Q}${HOSTCC} ${OBJECTS} ${DOIMAGE_LD_FLAGS} -o $@
+	${Q}$(host-cc) ${OBJECTS} ${DOIMAGE_LD_FLAGS} -o $@
 	@echo
 	@echo "Built $@ successfully"
 	@echo
 
 %.o: %.c Makefile
 	@echo "  HOSTCC  $<"
-	${Q}${HOSTCC} -c ${HOSTCCFLAGS} ${INCLUDE_PATHS} $< -o $@
+	${Q}$(host-cc) -c ${HOSTCCFLAGS} ${INCLUDE_PATHS} $< -o $@
 
 clean:
 	${Q}${RM} ${PROJECT}