drm/bridge: lt8912b: Add header file <linux/gpio/consumer.h>

If CONFIG_DRM_LONTIUM_LT8912B=m, the following errors will be seen while
compiling lontium-lt8912b.c

drivers/gpu/drm/bridge/lontium-lt8912b.c: In function
‘lt8912_hard_power_on’:
drivers/gpu/drm/bridge/lontium-lt8912b.c:252:2: error: implicit
declaration of function ‘gpiod_set_value_cansleep’; did you mean
‘gpio_set_value_cansleep’? [-Werror=implicit-function-declaration]
  gpiod_set_value_cansleep(lt->gp_reset, 0);
  ^~~~~~~~~~~~~~~~~~~~~~~~
  gpio_set_value_cansleep
drivers/gpu/drm/bridge/lontium-lt8912b.c: In function ‘lt8912_parse_dt’:
drivers/gpu/drm/bridge/lontium-lt8912b.c:628:13: error: implicit
declaration of function ‘devm_gpiod_get_optional’; did you mean
‘devm_gpio_request_one’? [-Werror=implicit-function-declaration]
  gp_reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
             ^~~~~~~~~~~~~~~~~~~~~~~
             devm_gpio_request_one
drivers/gpu/drm/bridge/lontium-lt8912b.c:628:51: error: ‘GPIOD_OUT_HIGH’
undeclared (first use in this function); did you mean ‘GPIOF_INIT_HIGH’?
  gp_reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
                                                   ^~~~~~~~~~~~~~
                                                   GPIOF_INIT_HIGH

Signed-off-by: Zhang Jianhua <zhangjianhua18@huawei.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210408093822.207917-1-zhangjianhua18@huawei.com