ltq-vdsl-app: fix -Wundef warnings

ltq-vdsl-app: fix -Wundef warnings

The following warnings are shown during build:

/usr/include/vdsl/cmv_message_format.h:33:6: warning: "MEI_SUPPORT_DEBUG_STREAMS" is not defined, evaluates to 0 [-Wundef]
 #if (MEI_SUPPORT_DEBUG_STREAMS == 1)
      ^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/vdsl/drv_mei_cpe_interface.h:2256:6: warning: "MEI_SUPPORT_OPTIMIZED_FW_DL" is not defined, evaluates to 0 [-Wundef]
 #if (MEI_SUPPORT_OPTIMIZED_FW_DL == 1)
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~

The headers are provided by the MEI driver, but the defines are never
set by the vdsl app. While the struct with the
MEI_SUPPORT_OPTIMIZED_FW_DL conditional isn't used by the vdsl app,
however CMV_USED_PAYLOAD_8BIT_SIZE which value depends on
MEI_SUPPORT_DEBUG_STREAMS is.

Since the MEI driver doesn't provide an autogenerated header with
compile flags, the flags are hardcoded for the vdsl app.

Set them for the MEI driver as well, to indicate a relation to the
values used for the vdsl app and to be not surprised by a changed
default in case the MEI driver gets updated. Use the current default
values defined in the MEI driver.

Signed-off-by: Mathias Kresin <dev@kresin.me>