vl: fix [memory] section with -readconfig

vl: fix [memory] section with -readconfig

The -M memory.* options do not have magic applied to them like the -m
option, namely no "M" (for mebibytes) is tacked at the end of a suffixless
value for "-M memory.size".

This magic is performed by parse_memory_options, and we have to do it for
both "-m" and the [memory] section of a config file.  Storing [memory]
sections directly to machine_opts_dict changed the meaning of

    [memory]
      size = "1024"

in a -readconfig file from 1024MiB to 8KiB (1024 Bytes rounded up to
8KiB silently).  To avoid this, the [memory] section has to be changed
back to QemuOpts (combining [memory] and "-m" will work fine thanks to
.merge_lists being true).

Change parse_memory_options() so that, similar to the older function
set_memory_options(), it operates after command line parsing is done;
and also call it where set_memory_options() used to be.

Note, the parsing code uses exit(1) instead of exit(EXIT_FAILURE) to
match neighboring code.

Reported-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Fixes: ce9d03fb3f ("machine: add mem compound property", 2022-05-12)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>