[TOPI] Expose mem_scope from generic conv2d variants to be more reusable

[cbalint13]

This small PR enhances generic conv2d TOPI schedules to be even more reusable.

Changes:

1. Continues PR #6714 and expose memory scope via mem_scope
2. Enhanches schedule_conv_NCHWc_cpu_common_int8 and schedule_conv_NCHWc_cpu_1x1_int8

Does not change current behaviour, memory scope remains "global" by default.

Goal:

Flexibility and reusability of key generic schedules is desirable for targets, especially custom ISA/ASIC.
There are use-cases where cache memory is not directly visible ("local") but generic TOPI is still very useful as-is.

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Cc @masahi , @vinx13 , @ZihengJiang please help with the review.

Thank you,
~Cristian.

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