phy: freescale: pcie: explicitly add bitfield.h

kernel test robot complains about missing FIELD_PREP, so include
bitfield.h for that

drivers/phy/freescale/phy-fsl-imx8m-pcie.c:41:37: error: implicit declaration of function 'FIELD_PREP' [-Werror=implicit-function-declaration]
drivers/phy/freescale/phy-fsl-imx8m-pcie.c:41:41: error: implicit declaration of function 'FIELD_PREP' [-Werror=implicit-function-declaration]

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 1aa97b0022 ("phy: freescale: pcie: Initialize the imx8 pcie standalone phy driver")
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Richard Zhu <hongxing.zhu@nxp.com>
Link: https://lore.kernel.org/r/20211215060834.921617-1-vkoul@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/freescale/phy-fsl-imx8m-pcie.c

@@ -3,6 +3,7 @@
  * Copyright 2021 NXP
  */
 
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/io.h>
 #include <linux/iopoll.h>