KVM: arm64: Rationalise KVM banner output

We are not very consistent when it comes to displaying which mode
we're in (VHE, {n,h}VHE, protected or not). For example, booting
in protected mode with hVHE results in:

[    0.969545] kvm [1]: Protected nVHE mode initialized successfully

which is mildly amusing considering that the machine is VHE only.

We already cleaned this up a bit with commit 1f3ca702

 ("KVM:
arm64: print Hyp mode"), but that's still unsatisfactory.

Unify the three strings into one and use a mess of conditional
statements to sort it out (yes, it's a slow day).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240321173706.3280796-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>