build: Change .external_dummy to dummy

to better align with the arch, boards and drivers naming convention

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

Kconfig

@@ -1824,7 +1824,7 @@ endmenu
 # Support optionally including external code
 # into the OS build. EXTERNALDIR will be used
 # to either point to 'nuttx/external' or
-# 'nuttx/.external-dummy', if 'nuttx/external'
+# 'nuttx/dummy', if 'nuttx/external'
 # does not contain a Kconfig file
 
 config EXTERNALDIR

tools/Makefile.unix

@@ -68,7 +68,7 @@ APPDIR := $(realpath ${shell if [ -r $(CONFIG_APPS_DIR)/Makefile ]; then echo "$
 # so that main Kconfig can find it. Otherwise, we redirect it to a dummy Kconfig
 # This is due to kconfig inability to do conditional inclusion.
 
-EXTERNALDIR := $(shell if [ -r $(TOPDIR)/external/Kconfig ]; then echo 'external'; else echo '.external-dummy'; fi)
+EXTERNALDIR := $(shell if [ -r $(TOPDIR)/external/Kconfig ]; then echo 'external'; else echo 'dummy'; fi)
 
 # CONTEXTDIRS include directories that have special, one-time pre-build
 #   requirements.  Normally this includes things like auto-generation of

tools/Makefile.win

@@ -53,7 +53,7 @@ APPDIR := $(realpath ${shell if exist "$(CONFIG_APPS_DIR)\Makefile" echo $(CONFI
 # so that main Kconfig can find it. Otherwise, we redirect it to a dummy Kconfig
 # This is due to kconfig inability to do conditional inclusion.
 
-EXTERNALDIR := $(shell if [ -r $(TOPDIR)\external\Kconfig ]; then echo 'external'; else echo '.external-dummy'; fi)
+EXTERNALDIR := $(shell if [ -r $(TOPDIR)\external\Kconfig ]; then echo 'external'; else echo 'dummy'; fi)
 
 # CONTEXTDIRS include directories that have special, one-time pre-build
 #   requirements.  Normally this includes things like auto-generation of