dm: test: Add tests for the generic PHY uclass

Those tests check:
- the ability for a phy-user to get a phy based on its name or its index
- the ability of a phy device (provider) to manage multiple ports
- the ability to perform operations on the phy (init,deinit,on,off)
- the behavior of the uclass when optional operations are not implemented

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

test/dm/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_LED) += led.o
 obj-$(CONFIG_DM_MAILBOX) += mailbox.o
 obj-$(CONFIG_DM_MMC) += mmc.o
 obj-$(CONFIG_DM_PCI) += pci.o
+obj-$(CONFIG_PHY) += phy.o
 obj-$(CONFIG_POWER_DOMAIN) += power-domain.o
 obj-$(CONFIG_DM_PWM) += pwm.o
 obj-$(CONFIG_RAM) += ram.o