make: make install target behave as expected

Split the 'make install' target into two: install and dist. dist
retains the old make install behavior of building a "distribution"
release, with source files, build system, etc. install does what
one one expects -- installs into a tree in the filesystem, /usr/local
by default.

Change-Id: I0805681ac10f853ef94cdc3aa70981c6bea81b45
diff --git a/docs.mk b/docs.mk
index 3e7b5cd..868bcb9 100644
--- a/docs.mk
+++ b/docs.mk
@@ -47,8 +47,8 @@
 	@doxygen $<
 DOCS-yes += docs/html/index.html
 
-INSTALL-DOCS-yes = $(wildcard docs/html/*)
-INSTALL-DOCS-$(CONFIG_CODEC_SRCS) += $(addprefix src/,$(CODEC_DOX))
-INSTALL-DOCS-$(CONFIG_CODEC_SRCS) += src/libs.doxy_template
-INSTALL-DOCS-yes                  += CHANGELOG
-INSTALL-DOCS-yes                  += README
+DIST-DOCS-yes = $(wildcard docs/html/*)
+DIST-DOCS-$(CONFIG_CODEC_SRCS) += $(addprefix src/,$(CODEC_DOX))
+DIST-DOCS-$(CONFIG_CODEC_SRCS) += src/libs.doxy_template
+DIST-DOCS-yes                  += CHANGELOG
+DIST-DOCS-yes                  += README