KVM: SVM: Rename vmcb->nested_ctl to vmcb->misc_ctl

KVM: SVM: Rename vmcb->nested_ctl to vmcb->misc_ctl

The 'nested_ctl' field is misnamed. Although the first bit is for nested
paging, the other defined bits are for SEV/SEV-ES. Other bits in the
same field according to the APM (but not defined by KVM) include "Guest
Mode Execution Trap", "Enable INVLPGB/TLBSYNC", and other control bits
unrelated to 'nested'.

There is nothing common among these bits, so just name the field
misc_ctl. Also rename the flags accordingly.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260303003421.2185681-19-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>