fpga: dfl: add feature device infrastructure

fpga: dfl: add feature device infrastructure

This patch abstracts the common operations of the sub features and defines
the feature_ops data structure, including init, uinit and ioctl function
pointers. And this patch adds some common helper functions for FME and AFU
drivers, e.g. dfl_feature_dev_use_begin/end which are used to ensure
exclusive usage of the feature device file.

Signed-off-by: Tim Whisonant <tim.whisonant@intel.com>
Signed-off-by: Enno Luebbers <enno.luebbers@intel.com>
Signed-off-by: Shiva Rao <shiva.rao@intel.com>
Signed-off-by: Christopher Rauer <christopher.rauer@intel.com>
Signed-off-by: Kang Luwei <luwei.kang@intel.com>
Signed-off-by: Zhang Yi <yi.z.zhang@intel.com>
Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Alan Tull <atull@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>