Work around kernel bug in memfd

https://bugzilla.kernel.org/show_bug.cgi?id=217238
Use F_SEAL_FUTURE_WRITE instead of F_SEAL_WRITE to work around a bug in older kernels.

Also remove F_SEAL_SEAL because it's unnecessary in this context.

Fixes: 409846908
Bug: 410561771
Test: BitmapTest
Flag: com.android.graphics.hwui.flags.bitmap_use_memfd
Change-Id: I47a3ba9da06ae6cce2f91e2f808280bdc0a354fd