EFI secure boot VECTX related changes

When VECTX is enabled as a kernel option and non-EFI loaders are
built, many reads will fail due to the mis-match of whether
LOADER_VERIEXEC_VECTX or not in readin.h. Source that includes
bootstrap.h must ensure the kernel option agrees with the compile
time CFLAGS in the various make related files.

Submitted by: bret_ketchum@dell.com (original revision)
Reviewed by: sjg, bdrewery, dab, bret_ketchum@dell.com
MFC after: 1 week
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D29993