devel/efl: fix build on powerpc64 elfv2

Explicitly include altivec.h if AltiVec build is done.
Otherwise build with clang fails with:
lib/evas/common/evas_cpu.c:89:11: warning: implicit declaration of function 'vec_splat_u32' is invalid in C99 [-Wimplicit-function-declaration]

zero = vec_splat_u32(0);
       ^

lib/evas/common/evas_cpu.c:89:9: error: assigning to '__vector unsigned int' (vector of 4 'unsigned int' values) from incompatible type 'int'

zero = vec_splat_u32(0);
     ^ ~~~~~~~~~~~~~~~~

PR: 242233
Approved by: enlightenment (maintainer timeout)