Cosmetic fixes for build output

By default, the OP-TEE build shows abbreviated output similar to the Linux
kernel. This commit fixes a number of deviations/inconsistencies.

- Always print a command in uppercase, followed by the target file.
- Make sure commands and file paths are nicely aligned, with two leading spaces
to make command output/errors better stand out.
- Remove some duplicate slashes in file paths. We use the following rule:
variables that hold directory names such as $(arch-dir) or $(platform-dir)
always have a trailing slash. The 'subdirs' and 'incdirs' variables used in
sub-makefiles are an exception because doing otherwise would needlessly
clutter the sub-makefiles.
diff --git a/Makefile b/Makefile
index 78ecc19..c558c21 100644
--- a/Makefile
+++ b/Makefile
@@ -28,12 +28,12 @@
 
 .PHONY: clean
 clean:
-	@echo Cleaning
+	@echo '  CLEAN   .'
 	${q}rm -f $(cleanfiles)
 
 .PHONY: cscope
 cscope:
-	@echo Creating cscope database
+	@echo '  CSCOPE  .'
 	${q}rm -f cscope.*
 	${q}find $(PWD) -name "*.[chSs]" > cscope.files
 	${q}cscope -b -q -k