fpga: Define bitstream type based on command selection

fpga: Define bitstream type based on command selection

Clean up partial, full and compressed bitstream handling.
U-Boot supports full bitstream loading and partial
based on detection which is not 100% correct.
Extending fpga_load/fpga_loadbitstream() with one more
argument which stores bitstream type.

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