x86/vmx: Factor locate_msr_entry() out of vmx_find_msr() and vmx_add_msr()

x86/vmx: Factor locate_msr_entry() out of vmx_find_msr() and vmx_add_msr()

Instead of having multiple algorithms searching the MSR lists, implement a
single one.  It has the semantics required by vmx_add_msr(), to identify the
position in which an MSR should live, if it isn't already present.

There will be a marginal improvement for vmx_find_msr() by avoiding the
function pointer calls to vmx_msr_entry_key_cmp(), and a major improvement for
vmx_add_msr() by using a binary search instead of a linear search.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>