linker: arcmwdt: use preprocess opiton -E.

-P is an option that was inherited from the old MetaWare compiler.
[ccac foo.c -P] is actually a shortcut for: [ccac -E foo.c -o foo.i].
In new version of mwdt, -P option can't redirect the output. we need
to use -E option, which works in all versions.

-P:  Preprocess the file and write it to <src>.i (C) or
      <src>.ii(C++). No compilation is performed.

-E:  Run preprocessor only.

Signed-off-by: Watson Zeng <zhiwei@synopsys.com>