drm/i915: cleanup fixed-point wrappers naming

drm/i915: cleanup fixed-point wrappers naming

This patch make naming of fixed-point wrappers consistent
operation_<any_post_operation>_<1st operand>_<2nd operand>
also shorten the name for fixed_16_16 to fixed16

s/u32_to_fixed_16_16/u32_to_fixed16
s/fixed_16_16_to_u32/fixed16_to_u32
s/fixed_16_16_to_u32_round_up/fixed16_to_u32_round_up
s/min_fixed_16_16/min_fixed16
s/max_fixed_16_16/max_fixed16
s/mul_u32_fixed_16_16/mul_u32_fixed16
s/fixed_16_16_div/div_fixed16

Changes Since V1:
 - Split the patch in more logical patches (Maarten)
Changes Since V2:
 - Rebase

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170705143154.32132-4-mahesh1.kumar@intel.com