[BOLT] Support .plt.got section

Summary:
We decode the regular .plt section and we are able to perform
optimizations on it with -plt=hot or -plt=all, however, .plt.got
sections are not decoded by BOLT. This patch teaches BOLT how to read
them. They are created by the bfd linker whenever there is no need for
the dynamic linker to lazy-bind the symbol (when they are eagerly
resolved at binary load time). These entries are 8-byte sized instead of
16-byte sized like the regular PLT, and contain a single indirect call
instruction with 7 bytes and a nop.

(cherry picked from FBD17060515)