x86/cpu: KVM: Move macro to encode PAT value to common header

x86/cpu: KVM: Move macro to encode PAT value to common header

Move pat/memtype.c's PAT() macro to msr-index.h as PAT_VALUE(), and use it
in KVM to define the default (Power-On / RESET) PAT value instead of open
coding an inscrutable magic number.

No functional change intended.

Reviewed-by: Xiaoyao Li <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>