Add PPC4xx-HCU4 and HCU5 boards: Infrastructure

This series of patches adds support for 2 boards from Netstal Maschinen.

The HCU4 has a PPC405Gpr and
the HCU5 has a PPC440EPX.

The HCU4 has a somehow complicated flash setup, as the booteprom is
only 8 bits and the CFI 16 bits wide, which makes it impossible to use a more
elegant solution.

The HCU5 has only a booteprom as the whole code will be downloaded from a
different board which has HD, CD-ROM, etc and where all code is stored.

This is my third try. I incorporated all suggestions made by Wolfgang and Stefan.
Thanks them a lot.

Signed-off-by: Niklaus Giger <niklaus.giger@netstal.com>
diff --git a/CREDITS b/CREDITS
index 7af1b80..1af9c7f 100644
--- a/CREDITS
+++ b/CREDITS
@@ -160,6 +160,11 @@
 E: ThomasF@hyperion-entertainment.com
 D: Support for AmigaOne
 
+N: Niklaus Giger
+E: niklaus.giger@netstal.com
+D: Support for HCU(x) boards
+W: www.netstal.com
+
 N: Paul Gortmaker
 E: paul.gortmaker@windriver.com
 D: Support for WRS SBC8347/8349 boards