[SPIRV] Support Bool buffer argument

[masahi]

SPIR-V spec says we cannot physically address boolean buffers, but right now we are generating code like this:

%_runtimearr_bool = OpTypeRuntimeArray %bool
...
%_ptr_StorageBuffer_bool = OpTypePointer StorageBuffer %bool
...
         %36 = OpInBoundsAccessChain %_ptr_StorageBuffer_bool %16 %int_0 %24
         %37 = OpLoad %bool %36 None

This is generating garbage outputs. Actually we hit an error at

tvm/src/target/spirv/ir_builder.cc

Lines 130 to 131 in 1831c17

	int nbits = value_type.type.bits() * value_type.type.lanes();
	ICHECK_EQ(nbits % 8, 0);

so boolean buffers are not supported at all.

I updated SPIR-V codegen to make a char buffer when the input is a bool tensor, and add cast to bool after loading the char.

If this change looks good, I should probably update the visitor for storing bool buffer output as well.

This enables running the cumsum test on a boolean flag array, which is explicitly disabled for vulkan in #7572 due to the lack of this fix.

@tqchen @tmoreau89 @jwfromm

[jwfromm]

LGTM, thanks masa!

[masahi]

@tqchen please have a look, I'll update #7572 after this is merged, to enable the cumsum test on boolean input.

[tqchen]

Thanks @masahi @jwfromm