alpha: define get_cycles macro for arch-override

Alpha defines a get_cycles() function, but it does not do the usual
`#define get_cycles get_cycles` dance, making it impossible for generic
code to see if an arch-specific function was defined. While the
get_cycles() ifdef is not currently used, the following timekeeping
patch in this series will depend on the macro existing (or not existing)
when defining random_get_entropy().

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Acked-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

arch/alpha/include/asm/timex.h

@@ -28,5 +28,6 @@ static inline cycles_t get_cycles (void)
 	__asm__ __volatile__ ("rpcc %0" : "=r"(ret));
 	return ret;
 }
+#define get_cycles get_cycles
 
 #endif