drm: panel: fix excessive stack usage in td028ttec1_prepare

drm: panel: fix excessive stack usage in td028ttec1_prepare

With gcc -O3 in combination with the structleak plug, the compiler can
inline very aggressively, leading to rather large stack usage:

drivers/gpu/drm/panel/panel-tpo-td028ttec1.c: In function 'td028ttec1_prepare':
drivers/gpu/drm/panel/panel-tpo-td028ttec1.c:233:1: error: the frame size of 2768 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
 }

Marking jbt_reg_write_*() as noinline avoids the case where
multiple instances of this function get inlined into the same
stack frame and each one adds a copy of 'tx_buf'.

The compiler is clearly making some bad decisions here, but I
did not open a new bug report as this only happens in combination
with the structleak plugin.

This fixes mmtom ("init/Kconfig: enable -O3 for all arches")

Link: https://lore.kernel.org/lkml/CAK8P3a3jAnFZA3GFRtdYdg1-i-oih3pOQzkkrK-X3BGsFrMiZQ@mail.gmail.com/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org> [fix indent]
Link: https://patchwork.freedesktop.org/patch/msgid/20200108135116.3687988-1-arnd@arndb.de