Draft: util-app: expand `--checks` to accomodate aarch64 machines

This MR consists in two commits, expanding the --checks command to accomodate aarch64 machines:

Adapt cpu_vt_capability check to ARM

For ARM, let's check whether "Virtualization Host Extensions" is present as part of dmesg, as in:

[fidencio@dentola ~]$ dmesg | grep -i "Virtualization Host Extensions"
[    0.000000] CPU features: detected: Virtualization Host Extensions

I know, we could figure out the host architecture, pass it to check_cpu_vt_capability(), and then do a switch on those. However, I'd prefer only do that once we're sure on that the method used is correct and when we start implementing something similiar to other architectures as well.

Expand module_kvm_loaded check

Let's also take into consideration that the module may be builtin. This came up while playing with an ARM SBC, but may affect any other architecture as well.

Related: #702

Without this MR:

[fidencio@dentola gnome-boxes]$ gnome-boxes --checks
• The CPU is capable of virtualization: no
• The KVM module is loaded: no
• Libvirt KVM guest available: yes
• Boxes storage pool available: yes
• The SELinux context is default: yes

With this MR:

[fidencio@dentola gnome-boxes]$ ./build/src/gnome-boxes --checks
• The CPU is capable of virtualization: yes
• The KVM module is loaded: yes
• Libvirt KVM guest available: yes
• Boxes storage pool available: yes
• The SELinux context is default: yes

Tested & developed on a NVIDA Jetson NX Xavier, using Fedora 34 as the host OS.