Update free DSP ROM and coefficients to support GBA ucode

- coef: Explicitly set 23 different values that are used by GBA UCode,
  and tweaked overall parameters to more closely match those 23 values.
- irom: Moved a few functions to their proper places, updated BootUCode
  to configure DMA transfers using AX registers as well as IX registers
  (the GBA UCode uses this to do two sequential transfers in one call),
  and added partial functions used by GBA UCode.

All functions were reverse-engineered solely based off of observed
effects on the virtual machine: register states before-and-after, dmem
interactions, and DMA transfers. The specific coefficients were observed
being read from dmem, and must be exactly those values to function
properly. I have no knowledge of how the official ROM implements these
functions, or how it is implemented overall.

Tested with The Legend of Zelda: Four Swords Adventures, Final Fantasy
Crystal Chronicles, and Billy Hatcher and the Giant Egg (to download
ChuChu Rocket!).

docs/DSP/free_dsp_rom/generate_coefs.py

@@ -12,7 +12,7 @@ def convert_coefs(c):
 def pack_coefs(short_coefs):
     return b''.join(pack('>H', c) for c in short_coefs)
 
-x = linspace(-2, 2, 512, endpoint=False)
+x = linspace(-2, 2, 512, endpoint=True)
 
 w1 = hamming(512)
 w2 = kaiser(512, pi * 9/4)
@@ -23,5 +23,37 @@ coef_3 = [sinc(n)        for n in x] * w1
 
 short_coefs = convert_coefs(coef_1) + convert_coefs(coef_2) + convert_coefs(coef_3) + [0] * 512
 
+# needed for GBA ucode
+gba_coefs = (
+    (0x03b, 0x0065),
+    (0x043, 0x0076),
+    (0x0ca, 0x3461),
+    (0x0e2, 0x376f),
+    (0x1b8, 0x007f),
+    (0x1b8, 0x007f),
+    (0x1f8, 0x0009),
+    (0x1fc, 0x0003),
+    (0x229, 0x657c),
+    (0x231, 0x64fc),
+    (0x259, 0x6143),
+    (0x285, 0x5aff),
+    (0x456, 0x102f),
+    (0x468, 0xf808),
+    (0x491, 0x6a0f),
+    (0x5f1, 0x0200),
+    (0x5f6, 0x7f65),
+    (0x65b, 0x0000),
+    (0x66b, 0x0000),
+    (0x66c, 0x06f2),
+    (0x6fe, 0x0008),
+    (0x723, 0xffe0),
+    (0x766, 0x0273),
+)
+for (addr, value) in gba_coefs:
+    old_value = short_coefs[addr]
+    if old_value != value:
+        print("At %04x: replacing %04x with %04x (diff. of % #x)" % (addr, old_value, value, value - old_value))
+        short_coefs[addr] = value
+
 with open('dsp_coef.bin', 'wb') as f:
     f.write(pack_coefs(short_coefs))