xilinx: microblaze-generic: Do not keep xparameters.h in git

This removal should be the part of
"Merge tag 'v2013.07' into xilinx/master-next"
(sha1: 6978377d4b022d7fd9a8c6f720ebc2e5daaeb173)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>