dsp: file: Add encode req & decode resp for DfOpen command

Added encode/decode APIs for DfOpen command(0x01)
which is defined in DSP0242 Version 1.0.0 Section: 9.2.

Change-Id: I5a975a7ae2bbd4115898486984ad96016590b04b
Signed-off-by: Chau Ly <chaul@amperecomputing.com>
diff --git a/tests/dsp/meson.build b/tests/dsp/meson.build
index dd2b5b0..64acb94 100644
--- a/tests/dsp/meson.build
+++ b/tests/dsp/meson.build
@@ -2,6 +2,7 @@
     'dsp/base',
     'dsp/bios_table',
     'dsp/bios',
+    'dsp/file',
     'dsp/firmware_update',
     'dsp/fru',
     'dsp/pdr',