blackfin: Move blackfin watchdog driver out of the blackfin arch folder.

- Enable hw_watchdog_init() in watchdog.h if CONFIG_HW_WATCHDOG is defined.
- Move blackfin hw watchdog driver to the generic driver folder.
- Call hw_watchdog_init() from blackfin board init code.
- Reuse macro CONFIG_WATCHDOG_TIMEOUT_MSECS
- Update README.watchdog accordingly

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
diff --git a/arch/blackfin/cpu/start.S b/arch/blackfin/cpu/start.S
index 7155fc8..1c6ae35 100644
--- a/arch/blackfin/cpu/start.S
+++ b/arch/blackfin/cpu/start.S
@@ -32,6 +32,7 @@
 
 #include <config.h>
 #include <asm/blackfin.h>
+#include <asm/mach-common/bits/watchdog.h>
 #include <asm/mach-common/bits/core.h>
 #include <asm/mach-common/bits/pll.h>
 
@@ -65,20 +66,29 @@
 	p5.h = HI(COREMMR_BASE);
 
 #ifdef CONFIG_HW_WATCHDOG
-#ifndef __ADSPBF60x__
-# ifndef CONFIG_HW_WATCHDOG_TIMEOUT_START
-#  define CONFIG_HW_WATCHDOG_TIMEOUT_START 5000
-# endif
-	/* Program the watchdog with an initial timeout of ~5 seconds.
+	/* Program the watchdog with default timeout of ~5 seconds.
 	 * That should be long enough to bootstrap ourselves up and
 	 * then the common u-boot code can take over.
 	 */
+	r1 = WDDIS;
+# ifdef __ADSPBF60x__
+	[p4 + (WDOG_CTL - SYSMMR_BASE)] = r1;
+# else
+	W[p4 + (WDOG_CTL - SYSMMR_BASE)] = r1;
+# endif
+	SSYNC;
 	r0 = 0;
-	r0.h = HI(MSEC_TO_SCLK(CONFIG_HW_WATCHDOG_TIMEOUT_START));
+	r0.h = HI(MSEC_TO_SCLK(CONFIG_WATCHDOG_TIMEOUT_MSECS));
 	[p4 + (WDOG_CNT - SYSMMR_BASE)] = r0;
+	SSYNC;
+	r1 = WDEN;
 	/* fire up the watchdog - R0.L above needs to be 0x0000 */
-	W[p4 + (WDOG_CTL - SYSMMR_BASE)] = r0;
-#endif
+# ifdef __ADSPBF60x__
+	[p4 + (WDOG_CTL - SYSMMR_BASE)] = r1;
+# else
+	W[p4 + (WDOG_CTL - SYSMMR_BASE)] = r1;
+# endif
+	SSYNC;
 #endif
 
 	/* Turn on the serial for debugging the init process */