Fix BSX detection for games with 2 startups left

"0x8c" was missing in the list of valid startup codes.
fix directory browsing after setting the clock.

properly mask cwd address to 24 bits
lazy FPGA reconfiguration

save a couple of ms on warm reset if the FPGA does not need to be
reconfigured.
only load configuration on initial powerup
Additional config entries, preparations for config menu and cheats
FPGA/DSPx: fix MMIO write priority