uboot-phytec

x86: Add clarifications to the x86 README

* Explicitly list the targets supported in each section of the
instructions from the x86 README.

* Drop references to 'raw mode', in favor of 'bare mode'.

Signed-off-by: Igor Stoppa <igor.stoppa@intel.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>