um: Replace UML_ROUND_UP() with PAGE_ALIGN()

um: Replace UML_ROUND_UP() with PAGE_ALIGN()

Although UML_ROUND_UP() is defined in a shared header file, it
depends on the PAGE_SIZE and PAGE_MASK macros, so it can only be
used in kernel code. Considering its name is not very clear and
its functionality is the same as PAGE_ALIGN(), replace its usages
with a direct call to PAGE_ALIGN() and remove it.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20251027054519.1996090-4-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg <johannes.berg@intel.com>