target-arm: Implement AArch64 TCR_EL1

target-arm: Implement AArch64 TCR_EL1

Implement the AArch64 TCR_EL1, which is the 64 bit view of
the AArch32 TTBCR. (The uses of the bits in the register are
completely different, but in any given situation the CPU will
always interpret them one way or the other. In fact for QEMU EL1
is always 64 bit, but we share the state field because this
is the correct mapping to permit a future implementation of EL2.)
We also make the AArch64 view the 'master' as far as migration
and reset is concerned.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>