When using Freedreno's RD output facilities, enable prefixing any output or
trigger file with the string specified in the FD_RD_DUMP_TESTNAME environment
option. This is similar to how the TESTNAME env can be used with libwrap to
provide a more descriptive name for the output RD file.

These prefixes can be quite long, e.g. the longest test case name in Vulkan CTS
is above 250 characters. For that reason the output name string in the
fd_rd_output struct is now allocated on the heap, and any path building using
the output name has its on-stack string buffer enlarged.

Signed-off-by: Zan Dobersek <zdobersek@igalia.com>
Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <!28442>