unicore32: Remove unused HAVE_ARCH_PCI_SET_DMA_MASK definition

HAVE_ARCH_PCI_SET_DMA_MASK is unused, so remove the #define for it.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: GUAN Xuetao <gxt@mprc.pku.edu.cn>