add a makefile under project root directory

it can be used as following:
  make ==> to make hypervisor & devicemodel & tools
also modify tools makefile to support out-dir setting.

Signed-off-by: Minggui Cao <minggui.cao@intel.com>
Reviewed-by: Jack Ren <jack.ren@intel.com>

tools/acrn-manager/Makefile

@@ -1,5 +1,8 @@
+
+OUT_DIR ?= .
+
 all: acrnctl.c
-	gcc -o acrnctl acrnctl.c -I../../include -Wall -g
+	gcc -o $(OUT_DIR)/acrnctl acrnctl.c -I../../devicemodel/include -Wall -g
 
 clean:
 	rm -f acrnctl

tools/acrnlog/Makefile

@@ -1,5 +1,8 @@
+
+OUT_DIR ?= .
+
 all:
-	gcc -g acrnlog.c -o acrnlog -lpthread
+	gcc -g acrnlog.c -o $(OUT_DIR)/acrnlog -lpthread
 
 clean:
 	rm acrnlog

tools/acrntrace/Makefile

@@ -1,5 +1,8 @@
+
+OUT_DIR ?= .
+
 all:
-	gcc -o acrntrace acrntrace.c sbuf.c -I. -lpthread
+	gcc -o $(OUT_DIR)/acrntrace acrntrace.c sbuf.c -I. -lpthread
 
 clean:
 	rm acrntrace