build: expand SYSCONFDIR to absolute path
build: expand SYSCONFDIR to absolute path

The default value of sysconfdir is "${prefix}/etc", we need to expand
${prefix} to get a usable path in ifapi_config.c.

Signed-off-by: Jonas Witschel <87a164e5d00d5dcdd001e37b34ea8bcd3fc3a172@gmx.de>

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