fpga: add a few more .gitignore patterns

Some other things we really don't need...

fpga/.gitignore

@@ -3,6 +3,9 @@ output/*.map
 output/*.jdi
 output/*.pof
 output/*.jbc
+output/*.sld
 output_files/
 *.cdf
 *.stp
+.qsys_edit
+*.BAK.*