runqemu: add QB_KERNEL_CMDLINE

runqemu: add QB_KERNEL_CMDLINE

runqemu auto generating the KERNEL_CMDLINE values and specifying using
-append option to qemu boot command which will lead to override the
kernel_cmdline/bootargs which are specified in DTB when using -dtb option.
Add new macro QB_KERNEL_CMDLINE to specify not to add the runqemu
generated KERNEL_CMDLINE values instead use which are in the DTB if
value defined as 'none'.
Add provision to override bootargs using # runqemu bootparams="root=/dev/ram0"

Signed-off-by: Raju Kumar Pothuraju <raju.kumar-pothuraju@xilinx.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>