microblaze: Label local function static

Warnings found by sparse:
arch/microblaze/kernel/dma.c:157:5: warning: symbol
'dma_direct_mmap_coherent' was not declared. Should it be static?
arch/microblaze/kernel/kgdb.c:35:14: warning: symbol 'pvr' was not
declared. Should it be static?

Signed-off-by: Michal Simek <michal.simek@xilinx.com>