clk: imx: Make CLK_IMX8ULP select MXC_CLK

Building CLK_IMX8ULP without selecting MXC_CLK causes the following
build errors:

ld: drivers/clk/imx/clk-imx8ulp.o: in function `imx8ulp_clk_cgc2_init':
clk-imx8ulp.c:(.text+0xd0): undefined reference to `imx_ccm_lock'
ld: clk-imx8ulp.c:(.text+0x14f): undefined reference to `imx_clk_hw_pllv4'
ld: clk-imx8ulp.c:(.text+0x15a): undefined reference to `imx_ccm_lock'

Avoid this problem by making CLK_IMX8ULP select MXC_CLK.

Fixes: c43a801a

 ("clk: imx: Add clock driver for imx8ulp")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/20211006190008.1935051-1-festevam@gmail.com
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>