Makefile: help: BR2_DEFCONFIG for defconfig must be on command line

The help text says that BR2_DEFCONFIG will be used as input, but a
BR2_DEFCONFIG specified in the existing .config file will *not* be
used. So say explicitly that it must be specified on the command line.
Note that both "BR2_DEFCONFIG=... make defconfig" and
"make defconfig BR2_DEFCONFIG=..." will work.

While we're at it, add a semicolon to separate the two statements.

Note that this overflows the help text beyond 80 characters, but that
is already the case in many other lines.

Reported-by: Anisse Astier <anisse@astier.eu>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 27aa7ae6182b2c6f8246c46b827a48fc80ffdd62)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -1020,8 +1020,8 @@ help:
 	@echo '  silentoldconfig        - Same as oldconfig, but quietly, additionally update deps'
 	@echo '  olddefconfig           - Same as silentoldconfig but sets new symbols to their default value'
 	@echo '  randconfig             - New config with random answer to all options'
-	@echo '  defconfig              - New config with default answer to all options'
-	@echo '                             BR2_DEFCONFIG, if set, is used as input'
+	@echo '  defconfig              - New config with default answer to all options;'
+	@echo '                             BR2_DEFCONFIG, if set on the command line, is used as input'
 	@echo '  savedefconfig          - Save current config to BR2_DEFCONFIG (minimal config)'
 	@echo '  allyesconfig           - New config where all options are accepted with yes'
 	@echo '  allnoconfig            - New config where all options are answered with no'