package/mesa3d: add missing dependencies for imagination driver

package/mesa3d: add missing dependencies for imagination driver

The build of the following basic configuration enabling the
imagination Vulkan driver

BR2_aarch64=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_AARCH64_GLIBC_STABLE=y
BR2_PACKAGE_MESA3D=y
BR2_PACKAGE_MESA3D_VULKAN_DRIVER_IMAGINATION=y

fails with:

meson.build:847:3: ERROR: Feature llvm cannot be disabled: CLC requires LLVM

Adding just LLVM as a dependency is not enough, as then libclc is
needed, then LLVMSPIRVLib, then clangBasic, then the pco_clc tool.

In fact, like the Panfrost driver, building the Imagination driver
requires building host tools using host-mesa3d. To fix this we:

- Make the BR2_PACKAGE_MESA3D_OPENCL option selectable

- Make sure that BR2_PACKAGE_MESA3D_VULKAN_DRIVER_IMAGINATION depends
  on BR2_PACKAGE_MESA3D_LLVM and select
  BR2_PACKAGE_MESA3D_NEEDS_PRECOMP_COMPILER (the latter being needed to
  build host-mesa3d)

- Make sure the host-mesa3d builds imagination
  tools (-Dtools=imagination) and install
  pco_clc (HOST_MESA3D_INSTALL_PCO_CLC). This requires introducing
  HOST_MESA3D_TOOLS as a list of tools to build, which then gets used
  to construct the -Dtools argument, as we can now have both
  "panfrost" and "imagination" in this list.

With all this, the defconfig above builds successfully.

This has been broken since Buildroot commit
5e818c16a31a902ec29a250f920f43c76e2d9868, which introduced the vulkan
driver support.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>