build: Replace chain of AS_IF calls with one AS_CASE.
build: Replace chain of AS_IF calls with one AS_CASE.

No functional changes in this commit, just using more of the available
tools to save a few characters.

Signed-off-by: Philip Tricca <53a58e9d5471ed7186e9729c1e05c03a7332643a@twobit.org>

01org/TPM2.0-TSS,tpm2-software/tpm2-tss,01org/tpm2-tss,01org/TPM2.0-TSS,tpm2-software/tpm2-tss,tpm2-software/tpm2-tss,01org/TPM2.0-TSS,01org/TPM2.0-TSS,01org/tpm2-tss,01org/tpm2-tss