linuxkpi: Fix the definition of BITS_PER_LONG

Don't use LP64 to decide the value, as it gives the wrong result on
CHERI platforms. Just define it in terms of SIZEOF_LONG. Make a
similar adjustment for BITS_PER_LONG_LONG while here.

Reviewed by: bz, dumbbell, emaste
MFC after: 1 week
Sponsored by: CHERI Research Centre (EPSRC grant UKRI3001)
Differential Revision: https://reviews.freebsd.org/D53135