st/mesa: Add rgbx handling for fp formats

Add missing cases for fp32 and fp16 formats.

Fixes: c68334ff "st/mesa: add floating point formats in st_new_renderbuffer_fb()"
Signed-off-by: Kevin Strasser <kevin.strasser@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
10 jobs for !979 with add_rgbx_handling in 20 minutes and 36 seconds (queued for 17 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #354808
debian

00:00:22

 
  Build+Test
passed #354810
meson-clang

00:08:33

passed #354814
meson-clover

00:11:36

passed #354813
meson-main

00:05:20

passed #354809
meson-swr-glvnd

00:07:05

passed #354815
meson-vulkan

00:02:12

passed #354817
scons-llvm

00:03:41

passed #354816
scons-nollvm

00:02:34

passed #354811
scons-swr

00:04:59

passed #354812
scons-win64

00:05:53