try_msr_calibrate_tsc() is currently Intel-specific, and should not
execute on any other vendor's parts.

This keeps in sync with Linux kernel commit:
  ba82683: x86/tsc_msr: Identify Intel-specific code

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>