cpu/x86/tsc: Flip and rename TSC_CONSTANT_RATE to UNKNOWN_TSC_RATE

The x86 timers are a bit of a mess. Cases where different stages use
different counters and timestamps use different counters from udelays.

The original intention was to only flip TSC_CONSTANT_RATE Kconfig
to NOT_CONSTANT_TSC_RATE. The name would be incorrect though, those
counters do run with a constant rate but we just lack tsc_freq_mhz()
implementation for three platforms.

Note that for boards with UNKNOWN_TSC_RATE=y, each stage will have a
slow run of calibrate_tsc_with_pit(). This is easy enough to fix with
followup implementation of tsc_freq_mhz() for the platforms.

Implementations with LAPIC_MONOTONIC_TIMER typically will not have
tsc_freq_mhz() implemented and default to UNKNOWN_TSC_RATE. However,
as they don't use TSC for udelay() the slow calibrate_tsc_with_pit()
is avoided.

Because x86/tsc_delay.tsc was using two different guards and nb/via/vx900
claimed UDELAY_TSC, but pulled UDELAY_IO implementation, we also switch
that romstage to use UDELAY_TSC.

Change-Id: I1690cb80295d6b006b75ed69edea28899b674b68
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
---
M src/arch/x86/cpu.c
M src/arch/x86/timestamp.c
M src/cpu/intel/fsp_model_406dx/Kconfig
M src/cpu/intel/haswell/Kconfig
M src/cpu/intel/model_1067x/Kconfig
M src/cpu/intel/model_106cx/Kconfig
M src/cpu/intel/model_2065x/Kconfig
M src/cpu/intel/model_206ax/Kconfig
M src/cpu/intel/model_6ex/Kconfig
M src/cpu/intel/model_6fx/Kconfig
M src/cpu/intel/slot_1/Kconfig
M src/cpu/intel/socket_mPGA604/Kconfig
M src/cpu/qemu-x86/Kconfig
M src/cpu/via/nano/Kconfig
M src/cpu/x86/Kconfig
M src/cpu/x86/tsc/Makefile.inc
M src/cpu/x86/tsc/delay_tsc.c
M src/drivers/pc80/pc/i8254.c
M src/include/cpu/x86/tsc.h
M src/northbridge/via/vx900/Makefile.inc
M src/soc/amd/picasso/Kconfig
M src/soc/intel/apollolake/Kconfig
M src/soc/intel/baytrail/Kconfig
M src/soc/intel/braswell/Kconfig
M src/soc/intel/broadwell/Kconfig
M src/soc/intel/cannonlake/Kconfig
M src/soc/intel/denverton_ns/Kconfig
M src/soc/intel/fsp_baytrail/Kconfig
M src/soc/intel/fsp_broadwell_de/Kconfig
M src/soc/intel/icelake/Kconfig
M src/soc/intel/quark/Kconfig
M src/soc/intel/skylake/Kconfig
32 files changed, 43 insertions(+), 54 deletions(-)