entry/kvm: KVM: Move KVM details related to signal/-EINTR into KVM proper

entry/kvm: KVM: Move KVM details related to signal/-EINTR into KVM proper

Move KVM's morphing of pending signals into userspace exits into KVM
proper, and drop the @vcpu param from xfer_to_guest_mode_handle_work().
How KVM responds to -EINTR is a detail that really belongs in KVM itself,
and invoking kvm_handle_signal_exit() from kernel code creates an inverted
module dependency.  E.g. attempting to move kvm_handle_signal_exit() into
kvm_main.c would generate an linker error when building kvm.ko as a module.

Dropping KVM details will also converting the KVM "entry" code into a more
generic virtualization framework so that it can be used when running as a
Hyper-V root partition.

Lastly, eliminating usage of "struct kvm_vcpu" outside of KVM is also nice
to have for KVM x86 developers, as keeping the details of kvm_vcpu purely
within KVM allows changing the layout of the structure without having to
boot into a new kernel, e.g. allows rebuilding and reloading kvm.ko with a
modified kvm_vcpu structure as part of debug/development.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wei Liu <wei.liu@kernel.org>