vtime: Describe overriden functions in dedicated arch headers

If the arch overrides some generic vtime APIs, let it describe
these on a dedicated and standalone header. This way it becomes
convenient to include it in vtime generic headers without irrelevant
stuff in such a low level header.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/include/asm/cputime.h

@@ -13,9 +13,6 @@
 #include <asm/div64.h>
 
 
-#define __ARCH_HAS_VTIME_ACCOUNT
-#define __ARCH_HAS_VTIME_TASK_SWITCH
-
 /* We want to use full resolution of the CPU timer: 2**-12 micro-seconds. */
 
 typedef unsigned long long __nocast cputime_t;