[fb] Add default hard-coded font

For the fb driver to have a font before loading from disk is available,
create a hard-coded font as a byte array.

To create this, added a new scripts/psf_to_cpp.py which also refactored
out much of scripts/parse_font.py into a new shared module
scripts/fontpsf.py.

scripts/psf_to_cpp.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+
+from fontpsf import PSF2
+
+def print_header(filename):
+    font = PSF2.load(filename)
+
+    print("#pragma once")
+    print(f"// This file was autogenerated by psf_to_cpp.py from {font.filename}\n")
+
+    print(f"const uint8_t font_glyph_size = {font.charsize};")
+    print(f"const uint8_t font_glyph_width = {font.dimension[0]};")
+    print(f"const uint8_t font_glyph_height = {font.dimension[1]};")
+    print(f"const uint16_t font_glyph_count = {font.count};\n")
+
+    print('const uint8_t font_glyph_data[] = {')
+
+    for glyph in font:
+        print("    ", "".join([f"0x{b:02x}," for b in glyph.data]), end="")
+        print(" // {}".format(glyph.description()))
+
+    print("};")
+
+if __name__ == "__main__":
+    import sys
+    for filename in sys.argv[1:]:
+        print_header(filename)