x86: expose tsc's timer_monotonic_get() in SMM

The implementation of timer_monotonic_get() for the tsc
module was being guarded from SMM. Allow this to be
linked into SMM as the generic spi flash driver now needs
this support which can be included in SMM.

Change-Id: I3909edecac8de117922c4ea6c53e6e561f6f435b
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10187
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)

src/cpu/x86/tsc/delay_tsc.c

@@ -190,7 +190,7 @@ void udelay(unsigned us)
 	}
 }
 
-#if CONFIG_TSC_MONOTONIC_TIMER && !defined(__PRE_RAM__) && !defined(__SMM__)
+#if CONFIG_TSC_MONOTONIC_TIMER && !defined(__PRE_RAM__)
 #include <timer.h>
 
 static struct monotonic_counter {