ARM: mv78xx0: adjust init logic for ts-wxl to reflect single core dev

Original code was largely copy-pasted from the reference board code, adjust pcie initialiazation to reflect the TS-WXL using the single-core variant of this SoC.
Correct pcie_port_size to be a power of 2 as required.

Signed-off-by: Jeremy J. Peper <jeremy@jeremypeper.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>