package/mesa3d: unconditionally needs expat

package/mesa3d: unconditionally needs expat

mesa3d should only need expat for a limited set of drivers. However,
the condition in their meson.build is borked:

    required: not with_platform_android or with_any_broadcom or with_any_intel

So, as soon as the platform is not android, expat is required. If it
is not already present in the configuraiotn, then meson will try to be
helpful and will try to download its own copy under the table:

    Run-time dependency expat found: NO (tried pkgconfig and cmake)
    Looking for a fallback subproject for the dependency expat
    Downloading expat source from https://github.com/libexpat/libexpat/releases/download/R_2_2_5/expat-2.2.5.tar.bz2
    <urlopen error unknown url type: https>
    A fallback URL could be specified using source_fallback_url key in the wrap file

    ../O/build/mesa3d-20.3.3/meson.build:1366:2: ERROR: could not get https://github.com/libexpat/libexpat/releases/download/R_2_2_5/expat-2.2.5.tar.bz2 is the internet available?

Ideally, we would like to fix the condition in the meson.build, to drop
the spurious and dubious condition on the android platform. However it
is not totally obvious what the prupose was, and expat compiles quikly,
so we just add expat as an unconditional mandatory dependency.

Fixes:
    http://autobuild.buildroot.org/results/f71865771482b1d71d12e77767d236ca693785d5/
    http://autobuild.buildroot.org/results/98290b9681a38b3be820017823a4a4196d474476/
    ....

Reported-by: Titouan Christophe <titouanchristophe@gmail.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
[yann.morin.1998@free.fr:
  - make it a generic fix, not tied to freedreno, reported by Fabio
  - rewrite commit log to explain the root cause
  - also reported about virgl, by Titouan
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>