arm64: Add override for MPAM

As the message of the commit 09e6b306 ("arm64: cpufeature: discover
CPU support for MPAM") already states, if a buggy firmware fails to
either enable MPAM or emulate the trap as if it were disabled, the
kernel will just fail to boot.  While upgrading the firmware should be
the best solution, we have some hardware of which the vendor have made
no response 2 months after we requested a firmware update.  Allow
overriding it so our devices don't become some e-waste.

Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Cc: Mingcong Bai <jeffbai@aosc.io>
Cc: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Cc: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250602043723.216338-1-xry111@xry111.site


Signed-off-by: Will Deacon <will@kernel.org>