epson: update available waveforms

Signed-off-by: Guillaume Tucker <guillaume.tucker@plasticlogic.com>
mod_plepaper_epson: fix memory leak + tidy-up code

* free the epdc->dev string if it's not NULL (created with
  strdup so it's allocated by the module)
* move all control interface paths to a table and iterate over it
  instead of if-else spaghetti
* store the Epson e-paper control interface path in epdc->dev
  instead of the framebuffer device
* check the framebuffer id with "modelffb" and abort if it's
  different (necessary in auto mode)
mod_plepaper_imx: fix memory leak with epdc->dev string
epson: fix return value of `update' function

Return 0 if no error, instead of previous return value
of fprintf which is usually > 0 (number of characters
written...).
imx: update {get|set}_opt with latest list of options

* add handle for PLEP_CLEAR_ON_EXIT (not supported)
* make table with ioctl codes instead of switch statement
epson: implement set_opt to set hardware options

* implement epdc->set_opt function (no get_opt yet)
* only PLEP_CLEAR_ON_EXIT option is currently supported
* tidy-up epson_update function
epson: add basic support for synchronous update

* add wait_sync_update function to call the "sync" command
* when sync update enabled, wait for the driver to be idle before
  requesting an update and wait for it to then become busy before
  returning the update function
epson: implement wait_power function

* add wait_sync_power to wait for the display HV power supply to
  reach a given state (1 or 0)
* wait for the power to be off in update function when
  PLEP_WAIT_POWER_OFF option is enabled (before and after the
  update)
* implement epdc->wait_power to simply block until the ePDC has
  reached the given power status
ChangeLog v011 -> v012