perf tools: Add empty Build files for architectures lacking them

perf currently fails to build on MIPS as there is no
tools/perf/arch/mips/Build file.  Adding an empty file fixes this as
there are no MIPS-specific sources to build.

It looks like the same is needed for Alpha and PA-RISC, though I
haven't been able to test those.

Signed-off-by: Ben Hutchings <[email protected]>
Fixes: 5e8c0fb ("perf build: Add arch x86 objects building")
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: bwhacks

tools/perf/arch/alpha/Build

@@ -0,0 +1 @@
+# empty

tools/perf/arch/mips/Build

@@ -0,0 +1 @@
+# empty

tools/perf/arch/parisc/Build

@@ -0,0 +1 @@
+# empty