drm/gma500/gem: Add and rename some function parameter descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/gma500/gem.c:57:5: warning: no previous prototype for ‘psb_gem_create’ [-Wmissing-prototypes]
 drivers/gpu/drm/gma500/gem.c:59: warning: Function parameter or member 'stolen' not described in 'psb_gem_create'
 drivers/gpu/drm/gma500/gem.c:59: warning: Function parameter or member 'align' not described in 'psb_gem_create'
 drivers/gpu/drm/gma500/gem.c:110: warning: Function parameter or member 'file' not described in 'psb_gem_dumb_create'
 drivers/gpu/drm/gma500/gem.c:110: warning: Excess function parameter 'drm_file' description in 'psb_gem_dumb_create'
 drivers/gpu/drm/gma500/gem.c:135: warning: Excess function parameter 'vma' description in 'psb_gem_fault'

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181313.3431493-16-lee.jones@linaro.org