qemu: Switch to -accel

We currently use -machine accel=XXX which is just a syntax sugar
for -accel XXX. The former doesn't allow specifying arguments for
accelerator, because all arguments passed to -machine are
treated as arguments of machine itself.

The -accel argument was introduced in QEMU commit
v2.9.0-rc0~70^2~19 and since our minimum required version is
newer (2.11.0) we can safely assume its existence and use it
without any capability.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/233
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Tested-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>

tests/qemuxml2argvdata/cpu-host-model.x86_64-6.0.0.args

@@ -10,7 +10,8 @@ XDG_CONFIG_HOME=/tmp/lib/domain--1-QEMUGuest1/.config \
 -name guest=QEMUGuest1,debug-threads=on \
 -S \
 -object '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/tmp/lib/domain--1-QEMUGuest1/master-key.aes"}' \
--machine pc-q35-6.0,accel=kvm,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-machine pc-q35-6.0,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-accel kvm \
 -cpu EPYC-Rome,x2apic=on,tsc-deadline=on,hypervisor=on,tsc-adjust=on,stibp=on,arch-capabilities=on,ssbd=on,xsaves=on,cmp-legacy=on,amd-ssbd=on,virt-ssbd=on,rdctl-no=on,skip-l1dfl-vmentry=on,mds-no=on,pschange-mc-no=on \
 -m 214 \
 -object '{"qom-type":"memory-backend-ram","id":"pc.ram","size":224395264}' \