[PATCH][PPC32] Fix mv64x60 register relocation bug in bootwrapper

The gt64260 looks at the highest 20 bits while the mv64[34]60 looks at 
only the highest 16 bits when determining the base address for the 
bridge's registers.  This patch adds support for both.

Please apply.

Signed-off-by: Nate Case <redacted>
Signed-off-by: Mark A. Greer <redacted>
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