Add NarrowRocketCache config fragment

[jerryz123]

For configs with wide SBUS, a narrow rocket cache is easier to PD, and does not incur any performance loss usually

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

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• Did you set main as the base branch?
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[SeahK]

worked, thanks!