libdrm: reduce number of reallocations in drmModeAtomicAddProperty

When calling drmModeAtomicAddProperty allocation of memory happens as
needed in increments of 16 elements. This can be very slow if there are
multiple properties to be updated in an Atomic Commit call.

Increase this to as many as can fit in a memory PAGE to avoid having to
reallocate memory too often.

Bug: 111047515
Change-Id: I043db1e7608b0a606adf1a6e468c90734372f363