m68k: Add infrastructure for machine-specific random_get_entropy()

On m68k, get_cycles() (the default implementation for random_get_entropy())
always returns zero, providing no entropy for the random driver.

Add a hook where platforms can provide their own implementation, and wire
it up in the infrastructure provided by commit
61875f30daf60305712e25b209ef41ced2635bad ("random: allow architectures to
optionally define random_get_entropy()").

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/include/asm/timex.h

@@ -28,4 +28,14 @@ static inline cycles_t get_cycles(void)
 	return 0;
 }
 
+extern unsigned long (*mach_random_get_entropy)(void);
+
+static inline unsigned long random_get_entropy(void)
+{
+	if (mach_random_get_entropy)
+		return mach_random_get_entropy();
+	return 0;
+}
+#define random_get_entropy	random_get_entropy
+
 #endif

arch/m68k/kernel/time.c

@@ -28,6 +28,10 @@
 #include <linux/timex.h>
 #include <linux/profile.h>
 
+
+unsigned long (*mach_random_get_entropy)(void);
+
+
 /*
  * timer_interrupt() needs to keep up the real-time clock,
  * as well as call the "xtime_update()" routine every clocktick