[ARM]add armv7 fp16 op conv5x5s1 conv5x5s2 conv3x3s2_direct

[lxwlaq]

3×3 s2 direct

conv	fp32	fp16	rate
input:1×4×64×64; weight:24×4×3×3	0.0727	0.04976	31.6%
input:1×4×128×128; weight:40×4×3×3	0.40227	0.232	42.2%
input:1×4×256×256; weight:40×4×3×3	1.57216	0.8753	44.5%
input:1×8×320×320; weight:40×8×3×3	4.58387	2.4304	46.9%

conv	fp32	fp16	rate
input:1×3×224×224; weight:24×3×3×3	0.76278	0.33987	55.5%
input:1×3×480×480; weight:24×3×3×3	3.605	1.50867	58.3%
input:1×3×256×256; weight:24×3×3×3	0.99461	0.43739	56.5%
input:1×3×320×320; weight:24×3×3×3	1.57998	0.67347	57.3%

5×5 depthwise

conv	fp32	fp16	rate
input:1×96×28×28 stride=1	0.22275	0.19064	14.4%
input:1×96×56×56 stride=1	0.85113	0.78724	8.2%
input:1×72x56×56 stride=1	0.63895	0.59116	7.8%
input:1×240×28×28 stride=1	0.50349	0.47392	6.0%

conv	fp32	fp16	rate
input:1×96×28×28 stride=2	0.17035	0.07006	58.8%
input:1×96×56×56 stride=2	0.75981	0.27707	63.5%
input:1×72x56×56 stride=2	0.57125	0.20434	64.9%
input:1×240×28×28 stride=2	0.42145	0.18061	57.1%

[paddle-bot-old]

Thanks for your contribution!

[chenjiaoAngel]

这两个指令可以插入几条其他指令，减少冲突

[chenjiaoAngel]

同上

[chenjiaoAngel]

同上

[chenjiaoAngel]

同上

[chenjiaoAngel]

同上

[chenjiaoAngel]

LGTM