Persimmon: Fix warning, enable warnings as errors

 - Fix redefinition warning for SB_GPIO_REG50 introduced in commit
     fa8702cf - http://review.coreboot.org/#/c/2446/
     Persimmon: adapt PCIe reset code copied from Inagua to actually
                 match Persimmon
     The warning being fixed is:
        SB800.h:1491, GNU Compiler 4 (gcc), Priority: Normal
        "SB_GPIO_REG50" redefined [enabled by default]

 - Enable warnings as errors so no more warnings will be accidentally
     committed.

Change-Id: Ib443b2bd2067f0b7d5f93f79170899a0f8f61060
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/2494
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
2 files changed