Cosmetic fixes for build output

[jforissier]

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.

[jbech-linaro]

+1, I like this a lot (been thinking about doing similar changes also). The only thing that nags me is that we loose the / after $(platform-dir) and friends in the actual makefiles. Sure there shouldn't be double slashes when compiling, so this is better. But I think I'd prefer that $(platform-dir) and friends don't have trailing slash. But hey, this is just a minor comment from my side, so I don't argue against merging this patch. So again +1.

[jforissier]

Well, the reason why I chose to keep the trailing slash in the variable is that the $(dir...) function always returns a string terminated with a slash. So, you would have to use $(patsubst %/,%, $(dir ...)) every time you want to extract a directory name from a path.

[jenswi-linaro]

+1

[pascal-brand38]

+1
Please squash on top of master

[jforissier]

Rebased.