ANDROID: KVM: arm64: Increase size of FF-A buffer

As it turns out, the kernel's DMA code doesn't enforce the
SG_MAX_SEGMENTS limit on the number of elements in an sglist, which can
confuse the pKVM FF-A proxy which has a buffer sized to contain a
descriptor of at most SG_MAX_SEGMENTS constituents.

As the number of elements in an sglist doesn't seem to have an actual
upper bound, let's paper over the issue for now by increasing the size
of the pKVM buffer based on empirical 'measurements'. Longer term we
might need to make this value configurable on the kernel's cmdline, or
to rework the FF-A proxy to sanely handle large descriptors, although
this is not clear how at the time of writing.

Bug: 221256863
Signed-off-by: Quentin Perret <qperret@google.com>
Change-Id: If252f01bec8ae71c0fe1f7007a3ca7b037924c84
(cherry picked from commit a6b9536c)