Revert "spi: axi-spi-engine: move msg state to new struct"

This reverts commit cde20c41 which is
commit 7f970ecb upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I377fa732fca3535f1ff2d9fcc3bbfa5ab3208e37
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>