[Clang][BPF] Support record argument with direct values

Currently, record arguments are always passed by reference by allocating
space for record values in the caller. This is less efficient for
small records which may take one or two registers. For example,
for x86_64 and aarch64, for a record size up to 16 bytes, the record
values can be passed by values directly on the registers.

This patch added BPF support of record argument with direct values
for up to 16 byte record size. If record size is 0, that record
will not take any register, which is the same behavior for x86_64
and aarch64. If the record size is greater than 16 bytes, the
record argument will be passed by reference.

Differential Revision: https://reviews.llvm.org/D132144