ARM: multi_v7_defconfig: make Samsung Exynos EHCI driver a module

Exynos EHCI driver is compiled as kernel built-in, but it requires Samsung
USB2 Generic PHY driver to operate properly, which is compiled as module.
Make the Exynos EHCI driver also a module, because having it built-in
makes no sense. Exynos OHCI, which also uses that PHY driver, is already
compiled as a module.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20201124083312.12356-1-m.szyprowski@samsung.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

arch/arm/configs/multi_v7_defconfig

@@ -773,7 +773,7 @@ CONFIG_USB_XHCI_TEGRA=m
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_EHCI_HCD_STI=y
 CONFIG_USB_EHCI_TEGRA=y
-CONFIG_USB_EHCI_EXYNOS=y
+CONFIG_USB_EHCI_EXYNOS=m
 CONFIG_USB_EHCI_MV=m
 CONFIG_USB_OHCI_HCD=y
 CONFIG_USB_OHCI_HCD_STI=y