vmm(4): vcpu_reset_regs_svm: allow reads of MSR_HWCR, MSR_PSTATEDEF(0)

vmm(4): vcpu_reset_regs_svm: allow reads of MSR_HWCR, MSR_PSTATEDEF(0)

Guests may need these MSRs to determine the TSC frequency on AMD
families 17h and 19h.

GP fault reported by weerd@, observed on "AMD EPYC 3201 8-Core Processor"
(17-01-02).  Same issue observed by Jesper Wallin on "AMD Ryzen PRO 3700U".
Tested by Jesper Wallin.

Link: https://marc.info/?l=openbsd-bugs&m=166721628323483&w=2
ok mlarkin@