rk3399: m0: Fix compiler warnings.

GCC complains for quite some versions, when compiling the M0 firmware
for Rockchip's rk3399 platform, about an invalid type of function 'main':

  warning: return type of 'main' is not 'int' [-Wmain]

This patch addresses this, by renaming the function to 'm0_main'.
Signed-off-by: Christoph Müllner <christophm30@gmail.com>
Change-Id: I10887f2bda6bdb48c5017044c264139004f7c785

plat/rockchip/rk3399/drivers/m0/src/dram.c

@@ -55,7 +55,7 @@ static void ddr_set_pll(void)
 	mmio_write_32(CRU_BASE + CRU_DPLL_CON3, PLL_MODE(PLL_NORMAL_MODE));
 }
 
-__attribute__((noreturn)) void main(void)
+__attribute__((noreturn)) void m0_main(void)
 {
 	mmio_setbits_32(PHY_REG(0, 927), (1 << 22));
 	mmio_setbits_32(PHY_REG(1, 927), (1 << 22));

plat/rockchip/rk3399/drivers/m0/src/startup.c

@@ -23,7 +23,7 @@ void WEAK svc_handler(void);
 void WEAK pend_sv_handler(void);
 void WEAK systick_handler(void);
 
-extern int main(void);
+extern int m0_main(void);
 
 /* Function prototypes */
 static void default_reset_handler(void);
@@ -59,12 +59,12 @@ void (* const g_pfnVectors[])(void) = {
  * This is the code that gets called when the processor first
  * starts execution following a reset event. Only the absolutely
  * necessary set is performed, after which the application
- * supplied main() routine is called.
+ * supplied m0_main() routine is called.
  */
 static void default_reset_handler(void)
 {
 	/* call the application's entry point */
-	main();
+	m0_main();
 }
 
 /**

plat/rockchip/rk3399/drivers/m0/src/suspend.c

@@ -11,7 +11,7 @@
 
 #define SCR_SLEEPDEEP_SHIFT	(1 << 2)
 
-__attribute__((noreturn)) void main(void)
+__attribute__((noreturn)) void m0_main(void)
 {
 	unsigned int status_value;