There are no differences in alignment between regular and sealed
capabilities on current architectures and even if there were there
is little value in putting this support in the kernel where callers
who need to seal values returned by mmap() will be highly CHERI-aware.

Kernel reservation managment code takes care of alignment (and size)
rounding for CheriABI binaries.  Hybrid binaries that need CHERI
alignment can, and for length must, do their own rounding in code that
will already be CHERI-aware.