llvmpipe: change LP_MAX_SHADER_INSTRUCTIONS limit definition.

When the limit was changed to be defined in terms of LP_MAX_SHADER_VARIANTS
(75f1fea14f) when it was increased, this
inadvertently lowered the limit in some branches (that have a lower
LP_MAX_SHADER_VARIANTS number) when merged. So, make sure the limit is always
at least the number it once was.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/drivers/llvmpipe/lp_limits.h

@@ -78,8 +78,10 @@
 /**
  * Max number of instructions (for all fragment shaders combined per context)
  * that will be kept around (counted in terms of llvm ir).
+ * Note: the definition looks odd, but there's branches which use a different
+ * number of max shader variants.
  */
-#define LP_MAX_SHADER_INSTRUCTIONS (512*LP_MAX_SHADER_VARIANTS)
+#define LP_MAX_SHADER_INSTRUCTIONS MAX2(128*1024, 512*LP_MAX_SHADER_VARIANTS)
 
 /**
  * Max number of setup variants that will be kept around.