templates: split syslinux templates to reduce diverting

A new common template called help.cfg has been included to avoid help
keys to be duplicated while prompt.cfg has been changed to be specific
to each mode since it has different requirements for initial text to
be displayed.

Other minor fixes were also been done during the spliting and then
included on this patch too.

templates/syslinux/common/help.cfg

@@ -1,8 +1,3 @@
-prompt 1
-display boot.txt
-timeout 0
-include menu.cfg
-
 f1 f1.txt
 f2 f2.txt
 f3 f3.txt

templates/syslinux/common/menu.cfg

@@ -1,5 +1,3 @@
-default live
-
 LINUX_LIVE
 
 LINUX_INSTALL

templates/syslinux/common/syslinux.cfg

@@ -1,6 +1,3 @@
 include header.cfg
 include menu.cfg
 include footer.cfg
-DISPLAY boot.txt
-
-PROMPT 1

templates/syslinux/menu/prompt.cfg

@@ -0,0 +1,6 @@
+prompt 1
+timeout 0
+default live
+display f1.txt
+include menu.cfg
+include help.cfg

templates/syslinux/normal/prompt.cfg

@@ -0,0 +1,6 @@
+prompt 1
+timeout 0
+default live
+display boot.txt
+include menu.cfg
+include help.cfg