pciconf: Use VM_MEMATTR_DEVICE on supported architectures

[kd]

Summary

Some architectures - armv7, armv8 and riscv use VM_MEMATTR_DEVICE when mapping device registers in kernel.
Do the same in pciconf when mmaping BARs.
On armada8k SoC all reads from BARs mapped with VM_MEMATTR_UNCACHEABLE return 0xffs.