Move VMX's MSR_TYPE_{R,W,RW} #defines to x86.h, as enums, so that they can
be used by common x86 code, e.g. instead of doing "bool write".

Opportunistically tweak the definitions to make it more obvious that the
values are bitmasks, not arbitrary ascending values.

No functional change intended.

Link: https://lore.kernel.org/r/20240802181935.292540-3-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>