soc: lpi: check if vote clk is enabled before accessing LPI GPIO

HW vote clock may fail to get enabled. Check if hw vote clk is
enabled in lpi_gpio_read and lpi_gpio_write to avoid kernel panic.

Change-Id: I077e5c61058d9d90be98ff3a0c0834049ad7e584
Signed-off-by: Meng Wang <mengw@codeaurora.org>