Add support for tracing 32-bit ARM EABI binaries on AArch64

Add support for tracing 32-bit ARM EABI binaries on AArch64

* defs.h [AARCH64]: Copy in the definition of arm_pt_regs and the
accessor macros, so it's possible to build on AArch64 without
ARM system headers.  Set SUPPORTED_PERSONALITIES to 2.
Define PERSONALITY0_WORDSIZE and PERSONALITY1_WORDSIZE.
Set DEFAULT_PERSONALITY to 1.
* linux/aarch64/errnoent1.h: New file, includes generic errnoent.h.
* linux/aarch64/ioctlent1.h: New file, includes generic ioctlent.h.
* linux/aarch64/signalent1.h: New file, includes generic signalent.h.
* linux/aarch64/syscallent1.h: Rename from linux/aarch64/syscallent.h.
* linux/aarch64/syscallent.h: New file, includes arm/syscallent.h.
* syscall.c [AARCH64]: Define aarch64_regs.
(update_personality) [AARCH64]: Add debug output.
(get_scno) [AARCH64]: Determine if we're in ARM or AArch64 mode by
checking the size of the returned uio structure from PTRACE_GETREGSET
and interpret the structure accordingly.
(get_syscall_result): Likewise.
(get_syscall_args): Merge the AArch64 and ARM sections so that on
AArch64 we can fall back to supporting the ARM personality.
(get_error): Likewise.

Signed-off-by: Steve McIntyre <steve.mcintyre@linaro.org>