libde265 @1.0.8: Allow +universal: add muniversal PortGroup

[barracuda156]

Lack of universal variant creates problems down the road. I tried to build imlib2 as +universal, it complained about libheif:

--->  Computing dependencies for imlib2.
Error: Cannot install imlib2 for the archs 'ppc ppc64' because
Error: its dependency libheif does not build for the required archs by default
Error: and does not have a universal variant.
Error: Follow https://guide.macports.org/#project.tickets if you believe there
is a bug.

In turn, libheif likewise claimed that its dependency libde265 can only build for ppc but not for ppc+ppc64. However it is unjustified: I added muniversal 1.0 to its Portfile, and with no patches it has built:

36-109:~ svacchanda$ port -v installed libde265
The following ports are currently installed:
  libde265 @1.0.8_0 requested_variants='' platform='darwin 9' archs='ppc' date='2022-03-08T04:21:56+0800'
  libde265 @1.0.8_0+universal (active) requested_variants='+universal' platform='darwin 9' archs='ppc ppc64' date='2022-04-06T03:29:23+0800'