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This patch resets EL2 and EL3 registers that have architecturally
UNKNOWN values on reset and that also provide EL2/EL3 configuration
and trap controls.

Specifically, the EL2 physical timer is disabled to prevent timer
interrups into EL2 - CNTHP_CTL_EL2 and CNTHP_CTL for AArch64 and AArch32,
respectively.

Additionally, for AArch64, HSTR_EL2 is reset to avoid unexpected traps of
non-secure access to certain system registers at EL1 or lower.

For AArch32, the patch also reverts the reset to SDCR which was
incorrectly added in a previous change.

Change-Id: If00eaa23afa7dd36a922265194ccd6223187414f
Signed-off-by: David Cunado <david.cunado@arm.com>