hv: vuart: fix the data type violations

- Fix the data type violations based on MISRA-C requirements
- Add '-fsigned-char' in Makefile to let the compiler treats 'char' be
   signed, like 'signed char'.
  Otherwise, the static checker treats 'char', 'signed char' and 'unsigned
   char' as three different types.
- Fix some minor coding style issues, such as TAB issues, line over 80
   characters issues and comments style

v1 -> v2:
 * fix the violation regarding to 'fifo_getchar'

Tracked-On: #861
Signed-off-by: Shiqing Gao <shiqing.gao@intel.com>
Reviewed-by: Junjie Mao <junjie.mao@intel.com>

hypervisor/include/debug/vuart.h

@@ -32,10 +32,10 @@
 
 struct fifo {
 	char *buf;
-	int rindex;	/* index to read from */
-	int windex;	/* index to write to */
-	int num;	/* number of characters in the fifo */
-	int size;	/* size of the fifo */
+	uint32_t rindex;	/* index to read from */
+	uint32_t windex;	/* index to write to */
+	uint32_t num;		/* number of characters in the fifo */
+	uint32_t size;		/* size of the fifo */
 };
 
 struct vuart {
@@ -52,7 +52,7 @@ struct vuart {
 
 	struct fifo rxfifo;
 	struct fifo txfifo;
-	int base;
+	uint16_t base;
 
 	bool thre_int_pending;	/* THRE interrupt pending */
 	bool active;