powerpc/44x: AMCC PPC460GT/EX PCI-E de-emphasis adjustment fix

During recent tests with PCI-E , it has been found the
DRV + De-Emphasis values are not optimum. These new values
are tested thouroughly.

Signed-off-by: Tirumala R Marri <tmarri@amcc.com>
Signed-off-by: Feng Kan <fkan@amcc.com>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>