Create a conf/machine/include/rockchip-wic.inc file to contain all the common
wic/wks things for easy inclusion by any MACHINEs that use wic for their image
creation.

NOTE: the wic image type of rock-pi-e changed from "wic.xz" to "wic" which
matches all the other meta-rockchip MACHINEs that use wic

The following variables were checked before and after to make sure they remain
correct/sensible:
- IMAGE_FSTYPES
- WKS_FILE_DEPENDS
- IMAGE_BOOT_FILES
- RK_CONSOLE_BAUD
- RK_CONSOLE_DEVICE
- RK_BOOT_DEVICE
- SERIAL_CONSOLES
- WICVARS

Build-tested for all currently-defined MACHINEs.

Boot-tested on the following boards to make sure they continue to boot to a
console correctly (core-image-base):
- tinker-board
- rock64
- rock-pi-4b
- rock-pi-e
- nanopi-m4-2gb

Signed-off-by: Trevor Woerner <twoerner@...>