spirv-tools: improve packaging

spirv-tools: improve packaging

spirv-tools is a set of libraries and some binaries that link to those
libraries, so inherit lib_package so that the binaries and the libraries
are packaged separately.

The lesspipe script hasn't needed bash since 2018[1], so remove the bash
dependency and package the script with the other binaries.

The build type unless specified is Debug, explicitly set RelWithDebInfo.

[1] spirv-tools f70e9e "tools/lesspipe: Allow generic shell (#2255)"

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>