fix(cpus): fix incorrect AMU trap settings for N2 CPU

The TAM bits of CPTR_EL2 and CPTR_EL3 are incorrectly set in the reset
handling sequence of the Neoverse N2 CPU. As these bits are set, any
access of AMU registers from EL0/EL1 and EL2 respectively are
incorrectly trapped to a higher EL. Fix this by clearing the TAM bits in
both the CPTR_EL2 and CPTR_EL3 registers.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I357b16dfc7d7367b8a0c8086faac28f3e2866cd8