kern_malloc: fold free and zfree together into one __always_inline func

[bz]

Summary

free() and zfree() are essentially the same copy and pasted code with
the extra explicit_bzero() (and kasan) calls. Add a bool to add the
extra functionality and make both functions a wrapper around the common
code and let the compiler do the optimization based on the bool input
when inlining.

No functional changes intended.

Suggested by: kib (in D45812)
Sponsored by: The FreeBSD Foundation
MFC after: 10 days

[kib]

sys/kern/kern_malloc.c

935

[bz]

Done locally.

[bz]

u_long -> uintptr_t

[markj]

sys/kern/kern_malloc.c

944

Hmm, I'm not sure why I put these kasan_mark() calls in zfree(), but they are unnecessary and can be removed.

[bz]

Remove kasan_mark calls as per @markj