scripts/mksysmap: use sed with in-line comments

It is not feasible to insert comments in a multi-line shell command.
Use sed, and move comments close to the code.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/mksysmap

@@ -11,32 +11,45 @@
 # Generate System.map (actual filename passed as second argument)
 # The following refers to the symbol type as per nm(1).
 
-# For System.map filter away:
-#   a - local absolute symbols
-#   U - undefined global symbols
-#   N - debugging symbols
-#   w - local weak symbols
-
 # readprofile starts reading symbols when _stext is found, and
 # continue until it finds a symbol which is not either of 'T', 't',
 # 'W' or 'w'.
 #
-# Ignored prefixes:
-#  $                    - local symbols for ARM, MIPS, etc.
-#  .L                   - local labels, .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc.
-#  __crc_               - modversions
-#  __kstrtab_           - EXPORT_SYMBOL (symbol name)
-#  __kstrtabns_         - EXPORT_SYMBOL (namespace)
+
+${NM} -n ${1} | sed >${2} -e "
+# ---------------------------------------------------------------------------
+# Ignored symbol types
 #
-# Ignored symbols:
-#  L0                   - for LoongArch?
-
-$NM -n $1 | grep -v		\
-	-e ' [aNUw] '		\
-	-e ' \$'		\
-	-e ' \.L'		\
-	-e ' __crc_'		\
-	-e ' __kstrtab_'	\
-	-e ' __kstrtabns_'	\
-	-e ' L0$'		\
-> $2
+
+# a: local absolute symbols
+# N: debugging symbols
+# U: undefined global symbols
+# w: local weak symbols
+/ [aNUw] /d
+
+# ---------------------------------------------------------------------------
+# Ignored prefixes
+#  (do not forget a space before each pattern)
+
+# local symbols for ARM, MIPS, etc.
+/ \$/d
+
+# local labels, .LBB, .Ltmpxxx, .L__unnamed_xx, .LASANPC, etc.
+/ \.L/d
+
+# CRC from modversions
+/ __crc_/d
+
+# EXPORT_SYMBOL (symbol name)
+/ __kstrtab_/d
+
+# EXPORT_SYMBOL (namespace)
+/ __kstrtabns_/d
+
+# ---------------------------------------------------------------------------
+# Ignored symbols (exact match)
+#  (do not forget a space before and '$' after each pattern)
+
+# for LoongArch?
+/ L0$/d
+"