tools/libxl: Don't prepare or save xc_config when soft resetting a domain

tools/libxl: Don't prepare or save xc_config when soft resetting a domain

xc_config is only used by xc_domain_create(), but by calling
libxl__arch_domain_{prepare,save}_config() we clobber the real settings with
the default settings.

Move all data and calls relating to xc_domain_create() into the path which
calls it.

As far as I can tell, soft_reset has always been broken for ARM domains using
LIBXL_GIC_VERSION_DEFAULT, which elicits a hard error out of
libxl__arch_domain_save_config(), and only works on x86 because this function
is a no-op.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>