softpipe: fix up NUM_ENTRIES confusion

softpipe: fix up NUM_ENTRIES confusion

There were two different NUM_ENTRIES #defines for the framebuffer
tile cache and the texture tile cache.  Rename the later to fix
the warnings:

In file included from sp_flush.c:40:0:
sp_tex_tile_cache.h:76:0: warning: "NUM_ENTRIES" redefined
sp_tile_cache.h:78:0: note: this is the location of the previous definition
In file included from sp_context.c:50:0:
sp_tex_tile_cache.h:76:0: warning: "NUM_ENTRIES" redefined
sp_tile_cache.h:78:0: note: this is the location of the previous definition

Also, replace occurances of NUM_ENTRIES with Element() macro to
be safer.

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