drm/panel: st7703: Fix timings when entering/exiting sleep

Fix flickering of the pinephone's XDB599 panel that happens after
resume.

Extend the delay after issuing the command to exit sleep mode from 60 to
120 msec as per the controller's specification.

Introduce a 120 msec delay after issuing the command to enter sleep
mode. This is needed in order for the controller to reliably finalize
the sleep in sequence before switching of power supply.

In contrast to the JH057N panel, the XBD599 panel does not require a 20
msec delay after initialization and exiting sleep mode. Therefore, move
the delay into the already existing device specific initialization
function.

The XDB599 does not require a 20 msec delay between the SETBGP and
SETVCOM commands. Therefore, remove the delay from the device specific
initialization function.

Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Cc: Ondrej Jirman <megi@xff.cz>
Reported-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Tested-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230213123238.76889-2-frank@oltmanns.dev