drm: deline a few large inlines in DRM code

This patch moves a few large functions from drm_memory.h
to drm_memory.c, with the following effect:

  text    data     bss     dec     hex filename
 46305    1304      20   47629    ba0d new/drm.ko
 46367    1304      20   47691    ba4b org/drm.ko
 12969    1372       0   14341    3805 new/i810.ko
 14712    1372       0   16084    3ed4 org/i810.ko
 16447    1364       0   17811    4593 new/i830.ko
 18198    1364       0   19562    4c6a org/i830.ko
 11875    1324       0   13199    338f new/i915.ko
 13025    1324       0   14349    380d org/i915.ko
 23936   29288       0   53224    cfe8 new/mga.ko
 27280   29288       0   56568    dcf8 org/mga.ko

Please apply.

Signed-off-by: Denis Vlasenko <vda@ilport.com.ua>
Signed-off-by: Dave Airlie <airlied@linux.ie>