KVM: Move vmx_vcpu_reset() out of vmx_vcpu_setup()

Split guest reset code out of vmx_vcpu_setup().  Besides being cleaner, this
moves the realmode tss setup (which can sleep) outside vmx_vcpu_setup()
(which is executed with preemption enabled).

[izik: remove unused variable]

Signed-off-by: Avi Kivity <avi@qumranet.com>