qemu: Enforce ACPI, UEFI requirements

Depending on the architecture, requirements for ACPI and UEFI can
be different; more specifically, while on x86 UEFI requires ACPI,
on aarch64 it's the other way around.

Enforce these requirements when validating the domain, and make
the error message more accurate by mentioning that they're not
necessarily applicable to all architectures.

Several aarch64 test cases had to be tweaked because they would
have failed the validation step otherwise.

tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-aavmf-virtio-mmio.xml

@@ -13,7 +13,6 @@
     <boot dev='hd'/>
   </os>
   <features>
-    <acpi/>
     <apic/>
     <pae/>
     <gic version='2'/>

tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-video-virtio-gpu-pci.xml

@@ -8,7 +8,6 @@
     <type arch='aarch64' machine='virt'>hvm</type>
   </os>
   <features>
-    <acpi/>
     <gic version='2'/>
   </features>
   <cpu mode='custom' match='exact' check='none'>

tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-virtio-pci-default.xml

@@ -13,7 +13,6 @@
     <boot dev='hd'/>
   </os>
   <features>
-    <acpi/>
     <apic/>
     <pae/>
     <gic version='2'/>

tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-virtio-pci-manual-addresses.xml

@@ -13,7 +13,6 @@
     <boot dev='hd'/>
   </os>
   <features>
-    <acpi/>
     <apic/>
     <pae/>
     <gic version='2'/>