usb: move CONFIG_USB_XHCI to Kconfig with renaming

Move CONFIG_USB_XHCI to defconfig files for all boards, renaming it
into CONFIG_USB_XHCI_HCD.

As commented in the help of "config USB_XHCI" entry, this has been
a TODO for a long time; now CONFIG_USB_XHCI_HCD and CONFIG_USB_XHCI
have been unified in favor of the former.

Note:
Some boards define CONFIG_USB_XHCI in their headers without
CONFIG_USB, which does not meet the "depends on" in Kconfig.
I added CONFIG_USB=y for those boards when converting.
Otherwise, they would fail to build.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/configs/ls1021aqds_nand_defconfig b/configs/ls1021aqds_nand_defconfig
index 9002a01..b3edd0a 100644
--- a/configs/ls1021aqds_nand_defconfig
+++ b/configs/ls1021aqds_nand_defconfig
@@ -21,6 +21,8 @@
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y
+CONFIG_USB=y
+CONFIG_USB_XHCI_HCD=y
 CONFIG_OF_LIBFDT=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y