panfrost: Use memctx for sysvals

panfrost: Use memctx for sysvals

8.74KB leaked over 52 calls from:
    0xffffbb5b9fc3
      in ??
    _mesa_hash_table_init
      at ../src/util/hash_table.c:163
      in /home/alyssa/rockchip_dri.so
    _mesa_hash_table_create
      at ../src/util/hash_table.c:186
    _mesa_hash_table_u64_create
      at ../src/util/hash_table.c:701
      in /home/alyssa/rockchip_dri.so
    panfrost_nir_assign_sysvals
      at ../src/panfrost/util/pan_sysval.c:130
      in /home/alyssa/rockchip_dri.so
    midgard_compile_shader_nir
      at ../src/panfrost/midgard/midgard_compile.c:2905
      in /home/alyssa/rockchip_dri.so

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Cc: mesa-stable
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6373>