[yaml2obj] Set p_align to the maximum sh_addralign of contained sections

The address difference between two sections in a PT_LOAD is a constant.
Consider a hypothetical case (pagesize can be very small, say, 4).

```
.text     sh_addralign=4
.text.hot sh_addralign=16
```

If we set p_align to 4, the PT_LOAD will be loaded at an address which
is a multiple of 4. The address of .text.hot is guaranteed to be a
multiple of 4, but not necessarily a multiple of 16.

This patch deletes the constraint

  if (SHeader->sh_offset == PHeader.p_offset)

Reviewed By: grimar, jhenderson

Differential Revision: https://reviews.llvm.org/D67260

llvm-svn: 371501