patch 9.1.0873: filetype: Vivado files are not recognized

Problem:  filetype: Vivado files are not recognized
Solution: detect '*.mss' files as 'mss' filetype
          (Wu, Zhenyu)

references:
https://docs.amd.com/r/2020.2-English/ug1400-vitis-embedded/Microprocessor-Software-Specification-MSS

closes: #15907

Signed-off-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_filetype.vim

@@ -507,6 +507,7 @@ def s:GetFilenameChecks(): dict<list<string>>
     mplayerconf: ['mplayer.conf', '/.mplayer/config', 'any/.mplayer/config'],
     mrxvtrc: ['mrxvtrc', '.mrxvtrc'],
     msidl: ['file.odl', 'file.mof'],
+    mss: ['file.mss'],
     msql: ['file.msql'],
     mojo: ['file.mojo', 'file.🔥'],
     msmtp: ['.msmtprc'],

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    873,
 /**/
     872,
 /**/