tools/power: turbostat: make Makefile a bit more capable

The turbostat Makefile is pretty simple, its output is placed in the
same directory as the source, the install rule has no concept of a
prefix or sysroot, and you can set CC to use a specific compiler but
not use the more familiar CROSS_COMPILE. By making a few minor changes
these limitations are removed while leaving the default behavior
matching what it used to be.

Example build with these changes:
make CROSS_COMPILE=i686-wrs-linux-gnu- DESTDIR=/tmp install

or from the tools directory
make CROSS_COMPILE=i686-wrs-linux-gnu- DESTDIR=/tmp turbostat_install

Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
Signed-off-by: Len Brown <len.brown@intel.com>

tools/power/x86/turbostat/Makefile

@@ -1,10 +1,22 @@
+CC		= $(CROSS_COMPILE)gcc
+BUILD_OUTPUT	:= $(PWD)
+PREFIX		:= /usr
+DESTDIR		:=
+
 turbostat : turbostat.c
 CFLAGS +=	-Wall
 CFLAGS +=	-I../../../../arch/x86/include/
 
+%: %.c
+	@mkdir -p $(BUILD_OUTPUT)
+	$(CC) $(CFLAGS) $< -o $(BUILD_OUTPUT)/$@
+
+.PHONY : clean
 clean :
-	rm -f turbostat
+	@rm -f $(BUILD_OUTPUT)/turbostat
 
-install :
-	install turbostat /usr/bin/turbostat
-	install turbostat.8 /usr/share/man/man8
+install : turbostat
+	install -d  $(DESTDIR)$(PREFIX)/bin
+	install $(BUILD_OUTPUT)/turbostat $(DESTDIR)$(PREFIX)/bin/turbostat
+	install -d  $(DESTDIR)$(PREFIX)/share/man/man8
+	install turbostat.8 $(DESTDIR)$(PREFIX)/share/man/man8