Revert "Lower the RAM requirement for hardware acceleration"

This reverts commit 498fd167c70847edfb2263ae09d05315f5a699de.
Revert "ActivityManager: memoize for performance"

This reverts commit 56739c20bc077e2e8e7cd903ba0a5a6cdb3f0b1a.
Lower the RAM requirement for hardware acceleration

There are legacy devices with about 365 MBytes of RAM
available to the kernel (HDPI with 512 MB RAM onboard).
Lowering the requirement value for available RAM allows
these devices to also use hardware acceleration, thus
making the UI a lot more responsive and fixing bugs like
this: https://dl.dropboxusercontent.com/u/16268774/Screenshots/Phone/Screenshot_2013-10-07-01-27-45.png
(notice the "shadow" is missing)

Change-Id: I0343ddbb3c7f95bed674b5852772ab819065ea69