phy: qcom-ufs: fix build error when the component is built as a module

Export the following functions in order to avoid build errors
when the component PHY_QCOM_UFS is compiled as a module:

ERROR: "ufs_qcom_phy_disable_ref_clk"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_enable_ref_clk"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_is_pcs_ready"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_disable_iface_clk"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_start_serdes"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_calibrate_phy"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_enable_dev_ref_clk"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_set_tx_lane_enable"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_disable_dev_ref_clk"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_save_controller_version"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
ERROR: "ufs_qcom_phy_enable_iface_clk"
	[drivers/scsi/ufs/ufs-qcom.ko] undefined!
make[1]: *** [__modpost] Error 1

Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
Reviewed-by: Gilad Broner <gbroner@codeaurora.org>
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>