r600g: rewrite FMASK allocation, fix FMASK texturing with 2 and 4 samples

This fixes and enables texturing with compressed MSAA colorbuffers
on Evergreen and Cayman. For the first time, multisample textures work
on Cayman.

This requires the libdrm flag RADEON_SURF_FMASK.

v2: require libdrm_radeon 2.4.45

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/configure.ac b/configure.ac
index 5bc8c94..eef4327 100644
--- a/configure.ac
+++ b/configure.ac
@@ -31,7 +31,7 @@
 
 dnl Versions for external dependencies
 LIBDRM_REQUIRED=2.4.24
-LIBDRM_RADEON_REQUIRED=2.4.44
+LIBDRM_RADEON_REQUIRED=2.4.45
 LIBDRM_INTEL_REQUIRED=2.4.38
 LIBDRM_NVVIEUX_REQUIRED=2.4.33
 LIBDRM_NOUVEAU_REQUIRED="2.4.33 libdrm >= 2.4.41"