util: update dumpstr

util: update dumpstr

Use a buffer of a limited size, use proper type for dump amount, avoid
hard-coding of byte counts, calculate output buffer size more accurately
and minimise its rewriting, pad offset with zeros in accordance
with expected output amount.

* defs.h (dumpstr): Change the type of len argument from int to
kernel_ulong_t.
* macros.h (ROUNDUP_DIV): New macro.
(ROUNDUP): Rewrite using ROUNDUP_DIV.
* util.c (ILOG2_ITER_): New macro.
(ilog2_64, ilog2_32): New functions.
(ilog2_klong): New macro, wrapper around ilog2_32/ilog2_64, so (potentially
more expensive) ilog2_64 is not used for ilog2 calculation
of a kernel_ulong_t-typed variable on architectures with 32-bit kernel long.
(dumpstr): Update.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>