Rename all APIs related to feature MSRs from get_msr_feature() to
get_feature_msr().  The APIs get "feature MSRs", not "MSR features".
And unlike kvm_{g,s}et_msr_common(), the "feature" adjective doesn't
describe the helper itself.

No functional change intended.

Link: https://lore.kernel.org/r/20240802181935.292540-6-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>