linux-user: Avoid redundant ENV_GET_CPU()

This fixes a mismerge in 874ec3c5b3821bb964f9f37b2f930f2a9ce51652.

Signed-off-by: Andreas Färber <afaerber@suse.de>
kvm: Change prototype of kvm_update_guest_debug()

Passing a CPUState pointer instead of a CPUArchState pointer eliminates
the last target dependent data type in sysemu/kvm.h.

It also simplifies the code.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>