php: disable FPM interface on Sparc
Building fails with "Sparc v8 and predecessors are not and will not be
supported (see bug report 53310)", so we disable FPM on Sparc.
Fixes:
http://autobuild.buildroot.net/results/6a86f6cf07f6b6dccd7bfaab6d7682f9faf3527b/
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>