Xtensa port: Added Xtensa internal timer configuration need by assembly files.

This is needed by next commit as some assembly files handling interrupts use
some options from this file.
This file is not included in next commit to separate code and build system
aptches.

Change-Id: Iff3a8019362599beb0c0058c3169480fa5183c1c
Signed-off-by: Mazen NEIFER <mazen@nestwave.com>