arm64/kvm: fix build issue on kvm debug

arm64/kvm: fix build issue on kvm debug

Add the header file asm/debug-monitors.h into debug-sr.c to fix the following bug
arch/arm64/kvm/hyp/debug-sr.c: In function ‘__debug_cond_save_host_state’:
arch/arm64/kvm/hyp/debug-sr.c:118:45: error: ‘DBG_MDSCR_KDE’ undeclared (first use in this function)
  if ((vcpu->arch.ctxt.sys_regs[MDSCR_EL1] & DBG_MDSCR_KDE) ||
                                             ^~~~~~~~~~~~~
arch/arm64/kvm/hyp/debug-sr.c:118:45: note: each undeclared identifier is reported only once for each function it appears in
arch/arm64/kvm/hyp/debug-sr.c:119:45: error: ‘DBG_MDSCR_MDE’ undeclared (first use in this function)
      (vcpu->arch.ctxt.sys_regs[MDSCR_EL1] & DBG_MDSCR_MDE))
                                             ^~~~~~~~~~~~~

Signed-off-by: Alex Shi <alex.shi@linaro.org>