Split VFP support in VFP2/3

Split VFP support in VFP2/3

BUG=none
TEST=Build with v8_can_use_vfp2_instructions=true on hardware with VFP2 but without VFP3, verify no crash

[lmcloughlin, 2012-07-20 21:03:12]

Uploading this since it's used for Raspberry Pi builds of Chromium to use VFP2
capability on the board (where VFP3 isn't supported).

[Yang, 2012-07-23 07:21:19]

Some comments. Adding Sven for more opinions. Generally, this patch opens up a
bunch of questions, and I'm not familiar enough with ARM to answer all of these:
- Do we support crankshaft for VFPv2 already, or only for VFPv3?
- Is there a documentation with a full list of what instructions are available
on VFPv3 and not on VFPv2?
- Have the assertions in all VFP instructions been consequently updated to the
correct requirement (VFPv2 or VFPv3)? Or is this only the first of many CLs?

https://chromiumcodereview.appspot.com/10796069/diff/1/src/arm/assembler-arm.cc
File src/arm/assembler-arm.cc (right):

https://chromiumcodereview.appspot.com/10796069/diff/1/src/arm/assembler-arm....
src/arm/assembler-arm.cc:1748: ASSERT(CpuFeatures::IsEnabled(VFP3) ||
CpuFeatures::IsEnabled(VFP2));
it seems to me that VFP3 is a superset of VFP2, VSTR is part of VFP2 and
CpuFeatures::IsEnabled(VFP3) implies CpuFeatures::IsEnabled(VFP3). So I would
like to suggest removing the redundant CpuFeatures::IsEnabled(VFP3).

https://chromiumcodereview.appspot.com/10796069/diff/1/src/arm/assembler-arm....
src/arm/assembler-arm.cc:2020: ASSERT(CpuFeatures::IsEnabled(VFP3));
From what I found, this is also available for VFPv2?
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489c/CJAEFGHE...

https://chromiumcodereview.appspot.com/10796069/diff/1/src/arm/assembler-arm....
src/arm/assembler-arm.cc:2034: ASSERT(CpuFeatures::IsEnabled(VFP3) ||
CpuFeatures::IsEnabled(VFP2));
Ditto.

https://chromiumcodereview.appspot.com/10796069/diff/1/src/arm/assembler-arm....
src/arm/assembler-arm.cc:2049: ASSERT(CpuFeatures::IsEnabled(VFP3));
Ditto. Also enable for VFP2?

[Yang, 2012-07-24 13:53:21]

This CL is superseded by http://codereview.chromium.org/10818026/