doc:style: do not use multiple empty lines

Enable LINE_SPACING but only check multiple blank lines now

Change-Id: I332d4d414a04eec8fc54b49d416a954d30592219
Signed-off-by: Mark Zhuang <mark.zhuang@spacemit.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8365
Reviewed-by: zapb <dev@zapb.de>
Reviewed-by: Jan Matyas <jan.matyas@codasip.com>
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

.checkpatch.conf

@@ -14,7 +14,6 @@
 --ignore ENOSYS
 --ignore FILE_PATH_CHANGES
 --ignore GERRIT_CHANGE_ID
---ignore LINE_SPACING
 --ignore LOGICAL_CONTINUATIONS
 --ignore MACRO_WITH_FLOW_CONTROL
 --ignore PARENTHESIS_ALIGNMENT

doc/manual/style.txt

@@ -45,7 +45,7 @@ OpenOCD project.
 - use TAB characters for indentation; do NOT use spaces.
 - displayed TAB width is 4 characters.
 - use Unix line endings ('\\n'); do NOT use DOS endings ('\\r\\n')
-- limit adjacent empty lines to at most two (2).
+- do NOT use multiple empty lines.
 - remove any trailing empty lines at the end of source files
 - do not "comment out" code from the tree nor put it within a block
   @code

tools/scripts/checkpatch.pl

@@ -4040,6 +4040,7 @@ sub process {
 			}
 		}
 
+if (!$OpenOCD) {
 # check for missing blank lines after struct/union declarations
 # with exceptions for various attributes and macros
 		if ($prevline =~ /^[\+ ]};?\s*$/ &&
@@ -4059,6 +4060,7 @@ sub process {
 				fix_insert_line($fixlinenr, "\+");
 			}
 		}
+} # !$OpenOCD
 
 # check for multiple consecutive blank lines
 		if ($prevline =~ /^[\+ ]\s*$/ &&
@@ -4073,6 +4075,7 @@ sub process {
 			$last_blank_line = $linenr;
 		}
 
+if (!$OpenOCD) {
 # check for missing blank lines after declarations
 # (declarations must have the same indentation and not be at the start of line)
 		if (($prevline =~ /\+(\s+)\S/) && $sline =~ /^\+$1\S/) {
@@ -4118,6 +4121,7 @@ sub process {
 				}
 			}
 		}
+} # !$OpenOCD
 
 # check for spaces at the beginning of a line.
 # Exceptions: