x86/cpufeatures: expose UMIP to HVM guests

x86/cpufeatures: expose UMIP to HVM guests

User-Mode Instruction Prevention (UMIP) is a security feature present in
new Intel Processors. With this feature, when the UMIP bit in CR4 set,
the following instructions cannot be executed if CPL > 0: SGDT, SIDT,
SLDT, SMSW, and STR. An attempt at such execution causes a general-
protection exception (#GP).

This patch simply adds necessary definitions to expose this feature to
hvm guests.

Signed-off-by: Boqun Feng (Intel) <boqun.feng@gmail.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>