[coreboot] Intel: How to share `tsc_freq.c` to select `UDELAY_TSC`

[Paul Menzel]

Dear coreboot folks,

after having looked at how to port Aaron’s commit

commit 7cb1ba9a61b244800eb65c08729f75d85a504de3
        Author: Aaron Durbin 
        Date:   Wed May 1 15:39:28 2013 -0500

haswell: use tsc for udelay()

Instead of using the local apic timer for udelay() use the
        tsc.
            That way SMM, romstage, and ramstage all use the same delay
            functionality.

Reviewed-on: http://review.coreboot.org/3169

to the i945-based T60, it looks like the following code

+#include <stdint.h>
        +#include <cpu/x86/msr.h>
        +#include <cpu/x86/tsc.h>
        +#include "cpu/intel/haswell/haswell.h"
        +
        +unsigned long tsc_freq_mhz(void)
        +{
        +       msr_t platform_info;
        +
        +       platform_info = rdmsr(MSR_PLATFORM_INFO);
        +       return HASWELL_BCLK * ((platform_info.lo >> 8) & 0xff);
        +}

is generic enough and can be used by the northbridges i945, i5000 and
Sandy Bridge as

#define MSR_PLATFORM_INFO               0xce

is true for the three of them.

So where should `tsc_freq.c` be put and how should the header be
included?

Thanks,

Paul