qemu-options: Deprecate -old-param command line option

qemu-options: Deprecate -old-param command line option

The '-old-param' command line option is specific to Arm targets; it
is very briefly documented as "old param mode".  What this option
actually does is change the behaviour when directly booting a guest
kernel, so that command line arguments are passed to the kernel using
the extremely old "param_struct" ABI, rather than the newer ATAGS or
even newer DTB mechanisms.

This support was added back in 2007 to support an old vendor kernel
on the akita/terrier board types:
 https://mail.gnu.org/archive/html/qemu-devel/2007-07/msg00344.html
Even then, it was an out-of-date mechanism from the kernel's
point of view -- the kernel has had a comment since 2001 marking
it as deprecated. As of mid-2024, the kernel only retained
param_struct support for the RiscPC and Footbridge platforms:
 https://lore.kernel.org/linux-arm-kernel/2831c5a6-cfbf-4fe0-b51c-0396e5b0aeb7@app.fastmail.com/

None of the board types QEMU supports need param_struct support;
mark this option as deprecated.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20250127123113.2947620-1-peter.maydell@linaro.org