hw/arm/boot: Add boot support for AArch64 processor

This commit adds support for booting a single AArch64 CPU by setting
appropriate registers. The bootloader includes placeholders for Board-ID
that are used to implement uniform indexing across different bootloaders.

Signed-off-by: Mian M. Hamayun <m.hamayun@virtualopensystems.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1385645602-18662-7-git-send-email-peter.maydell@linaro.org
[PMM:
 * updated to use ARMInsnFixup style bootloader fragments
 * dropped virt.c additions
 * use runtime checks for "is this an AArch64 core" rather than ifdefs
 * drop some unnecessary setting of registers in reset hook
]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
