FROMGIT: arm64: head.S: Initialise MPAM EL2 registers and disable traps

Add code to head.S's el2_setup to detect MPAM and disable any EL2 traps.
This register resets to an unknown value, setting it to the default
parititons/pmg before we enable the MMU is the best thing to do.

Kexec/kdump will depend on this if the previous kernel left the CPU
configured with a restrictive configuration.

If linux is booted at the highest implemented exception level el2_setup
will clear the enable bit, disabling MPAM.

Signed-off-by: James Morse <james.morse@arm.com>

Bug: 221768437
(cherry picked from commit fa0ff38f06b397d8a92d88eb8083c2c5a20ac87f
 git://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git

 mpam/snapshot/v5.16)
Change-Id: I2758f7f7b236d09a207e13d1165efb6887e8611a
Signed-off-by: Valentin Schneider <Valentin.Schneider@arm.com>
[bm: amended commit msg, dropped config option and switched to named labels]
Signed-off-by: Beata Michalska <beata.michalska@arm.com>