ppc4xx: AMCC PPC460GT/EX PCI-E de-emphasis adjustment fix

During recent PCI-E tests it has been found that current
driverl level and de-emphasis values are not set correctly.
After sweeping throgh all de-ephasis values, it was found that
0x130 is a right value. Where 0x13 is driver level and 0 is
de-emphasis.

Signed-off-by: Tirumala R Marri <tmarri@amcc.com>
Signed-off-by: Stefan Roese <sr@denx.de>