Add dummy definitions of the FPGA API functions for build testing.

v2: (1) Add a missing #endif to altera-pr-ip-core.h
    (2) Change conditional compilation tests to use #if
        IS_ENABLED(CONFIG_xxx) instead of #ifdef CONFIG_xxx to avoid
        compilation errors when the options are configured as modules.

1) fpga: altera-pr-ip: Add dummy definitions of API functions
2) fpga: bridge: Add dummy definitions of API functions
3) fpga: manager: Add dummy definitions of API functions
4) fpga: region: Add dummy definitions of API functions

 include/linux/fpga/altera-pr-ip-core.h |  8 +++
 include/linux/fpga/fpga-bridge.h       | 75 ++++++++++++++++++++++++++-
 include/linux/fpga/fpga-mgr.h          | 95 +++++++++++++++++++++++++++++++---
 include/linux/fpga/fpga-region.h       | 44 ++++++++++++++--
 4 files changed, 208 insertions(+), 14 deletions(-)