sim: bpf: fix testsuite due to linker warnings [PR sim/29954]

On a bpf-*-* testsuite fails:
	./ld/ld-new: warning: test has a LOAD segment with RWX permissions

Adjusting `--memory-size=10Mb' to the simulator bpf testsuite passes.

Tested on bpf-*-*:

Bug: https://sourceware.org/PR29954

sim/testsuite:
	* bpf/allinsn.exp (SIMFLAGS_FOR_TARGET): Adjust sim flags.