acpi: Use U-Boot version for OEM_REVISION

OEM_REVISION is 32-bit unsigned number. It should be increased only when
changing software version. Therefore it should not depend on build time.

Change calculation to use U-Boot version numbers and set this revision
to date number.

Prior this change OEM_REVISION was calculated from build date and stored in
the same format.

After this change macro U_BOOT_BUILD_DATE is not used in other files so
remove it from global autogenerated files and also from Makefile.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>