drm/i915: Check return value of drm_addmap()

Abort loading if this fails.
drm: Fix typo in comment in drm_memory.c
drm/radeon: Fix incompatibility between Linux and FreeBSD PAGE_MASK

On Linux:   PAGE_MASK = ~(PAGE_SIZE - 1)
On FreeBSD: PAGE_MASK = (PAGE_SIZE - 1)
drm/radeon: Fix incompatibility between Linux and FreeBSD PAGE_MASK

On Linux:   PAGE_MASK = ~(PAGE_SIZE - 1)
On FreeBSD: PAGE_MASK = (PAGE_SIZE - 1)