rockchip: rk3399-gru: Enable TPL_GPIO for bob and kevin

The PP1500 and PP3000 power rails must be on very early for the U-Boot
TPL banner to be shown on debug UART.

Enable TPL_GPIO Kconfig option for bob and kevin to allow use of
spl_gpio.h functions in TPL.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>