cpu/x86: Move calibrate_tsc_with_pit() to drivers/pc80

Change-Id: Ia8d8dc23ee0b51d62c83f5ba640b3a9aea4e744b
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36507
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/include/pc80/i8254.h

@@ -55,5 +55,6 @@
 #define PPCB_T2GATE     0x01    /* Bit 0 */
 
 void setup_i8254(void);
+unsigned long calibrate_tsc_with_pit(void);
 
 #endif /* PC80_I8254_H */