Several GCC warnings were getting generated on various compilers.  This
patch solves those warnings.

For various platforms, a uint32_t is not the same as an unsigned int. On
these platforms, printf("%x", (uint32_t)0) generates a warning.  Use the
<inttypes.h> formats (i.e. PRIx32) as formatters to silence these warnings.

There was also a security warning picked up by certain compilers when
calling printf(msg) in fernly-usb-loader.  This has been fixed.

Finally, lcd.c was refactored to fold the unused lcd_dat_slot() function
into the lcd_cmd_slot() function as a brand-new unified lcd_slot().

Signed-off-by: Sean Cross <xobs@kosagi.com>