staging: sm750fb: rename PANEL_PLL_CTRL_* fields to PLL_CTRL_*

Several PLL control registers have the same layout and therefore the
field definitions may be shared for those registers. Renaming
definitions of PANEL_PLL_CTRL_* fields to more generic PLL_CTRL_* will
allow reusing these definitions for other PLL control registers.

Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>