vmm svm: Add SVM_CTR* wrapper macros.

These macros are similar to VCPU_CTR* but accept a single svm_vcpu
pointer as the first argument instead of separate vm and vcpuid.

Reviewed by: corvink, markj
Differential Revision: https://reviews.freebsd.org/D37153

(cherry picked from commit fca494dad06242aa45d3e722f0c16b405dc8039c)