[libc][nfc] Include header for EFIAPI macro (#198876)

This file uses `EFIAPI`, but it's not included. It looks like
compilation currently succeeds because `EFI_SYSTEM_TABLE.h` is the only
header that includes `EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.h`, and it happens
to include `EFIAPI-macros.h` indirectly.

We will be adding Bazel rules for this file, and Bazel typically
requires all headers to be compilable on their own. This build error is
theoretically reproducable by running cmake build with
`-DCMAKE_VERIFY_INTERFACE_HEADER_SETS` if we had the appropriate
FILE_SETs defined.

GitOrigin-RevId: f755811bab9520fb52b6d531ea8a4ffcdae6b245