[yaml2obj] - Rename FileHeader::SH* fields.

In D83482 we agreed to name e_* fields that are used for overriding
values (like e_phoff) as EPh* (e.g. EPhOff).

Currently we have a set of e_sh* fields that are named inconsistently
with this rule. This patch renames all of them.

Differential revision: https://reviews.llvm.org/D83766