clocksource/drivers/arm_arch_timer: Workaround bcm2712 broken EL2 virtual timer

clocksource/drivers/arm_arch_timer: Workaround bcm2712 broken EL2 virtual timer

It appears that the bcm2712 SoC found in the relatively popular RPi5 has a
broken EL2 virtual timer.

Tthe reason why the timer isn't working is unknown (the timer is ticking,
but the interrupt never fires), and the SoC vendor doesn't communicate on
the reason why this isn't working, leaving users and maintainers in the
dark.

Paper over the issue by detecting the broken HW, falling back to the
physical timer instead, and let the user know about it.  Also taint the
kernel as the machine is definitely not compliant with the spec, and it's
unknown what else is wrong with it.

Reported-by: John <therealgraysky@proton.me>
Reported-by: Daniel Drake <dan@reactivated.net>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Gary Guo <gary@garyguo.net>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Cc: Daniel Lezcano <daniel.lezcano@kernel.org>
Link: https://patch.msgid.link/20260710080958.491620-1-maz@kernel.org