x86/msr: Switch between WRMSRNS and WRMSR with the alternatives mechanism

Per the discussion about FRED MSR writes with WRMSRNS instruction [1],
use the alternatives mechanism to choose WRMSRNS when it's available,
otherwise fallback to WRMSR.

Remove the dependency on X86_FEATURE_WRMSRNS as WRMSRNS is no longer
dependent on FRED.

[1] https://lore.kernel.org/lkml/15f56e6a-6edd-43d0-8e83-bb6430096514@citrix.com/



Use DS prefix to pad WRMSR instead of a NOP. The prefix is ignored. At
least that's the current information from the hardware folks.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240822073906.2176342-3-xin@zytor.com