[PATCH v6] linux,stdout-path helper

[Sascha Hauer]

The following adds a helper for matching the linux,stdout-path property
in the chosen node and makes use of it in the i.MX serial

This is a series originally created by me. It was hijacked and then abandoned
by Jean-Christophe for v5. I reverted the changes by Jean-Christophe since
they introduced changes to the devicetree binding. Instead I'd like to have
the existing binding implemented first before changing it.

Sascha

changes since v5:
- reverted changes from v4
- parse linux,stdoutpath property in of_alias_scan as suggested by Grant
changes since v4:
- add option support and check stdout-path too
changes since v3:
- move code from separate files to drivers/of/base.c and include/linux/of.h
changes since v2:
- move helper to OF core and make it independent of serial devices
changes since v1:
- move it out of the i.MX serial driver and make it generic for serial devices.