Merge tag 'bsd-user-for-9.1-pull-request' of gitlab.com:bsdimp/qemu into staging

bsd-user: Misc changes for 9.1 (I hope)

V2: Add missing bsd-user/aarch64/target.h

This patch series includes two main sets of patches. To make it simple to
review, I've included the changes from my student which the later changes depend
on. I've included a change from Jessica and Doug as well. I've reviewed them,
but more eyes never hurt.

I've also included a number of 'touch up' patches needed either to get the
aarch64 building, or to implmement suggestions from prior review cycles. The
main one is what's charitably described as a kludge: force aarch64 to use 4k
pages. The qemu-project (and blitz branch) hasn't had the necessary changes to
bsd-user needed to support variable page size.

Sorry this is so late... Live has conspired to delay me.

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# gpg: Good signature from "Warner Losh <wlosh@netflix.com>" [unknown]
# gpg:                 aka "Warner Losh <imp@bsdimp.com>" [unknown]
# gpg:                 aka "Warner Losh <imp@freebsd.org>" [unknown]
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# gpg:                 aka "Warner Losh <wlosh@bsdimp.com>" [unknown]
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* tag 'bsd-user-for-9.1-pull-request' of gitlab.com:bsdimp/qemu:
  bsd-user: Add target.h for aarch64.
  bsd-user: Add aarch64 build to tree
  bsd-user: Make compile for non-linux user-mode stuff
  bsd-user: Define TARGET_SIGSTACK_ALIGN and use it to round stack
  bsd-user: Sync fork_start/fork_end with linux-user
  bsd-user: Hard wire aarch64 to be 4k pages only
  bsd-user: Simplify the implementation of execve
  bsd-user:Add AArch64 improvements and signal handling functions
  bsd-user:Add set_mcontext function for ARM AArch64
  bsd-user:Add setup_sigframe_arch function for ARM AArch64
  bsd-user:Add get_mcontext function for ARM AArch64
  bsd-user:Add ARM AArch64 signal handling support
  bsd-user:Add ARM AArch64 support and capabilities
  bsd-user:Add AArch64 register handling and related functions
  bsd-user:Add CPU initialization and management functions

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>