How to use a Linker File with Keil uVision5 ARM?
On the Options for Target dialog, Linker tab, the Use Memory Layout from Target Dialog option determines whether your custom scatter file is used.  When Use Memory Layout from Target Dialog is checked, the linker uses information from the memory options selected on the Target tab.  (The toolchain uses the Target tab settings to automatically generate a scatter file, which is fed to the linker.)  You must uncheck Use Memory Layout from Target Dialog in order to use a custom scatter file specified on the Linker tab.

I believe scatter files typically have a .sct extension.  Was your bootload.ld written for the Keil toolchain or another?  If it was written for another toolchain then it probably won't work with the Keil toolchain unless you rewrite it to use the proper Keil scatter file syntax.

For an example scatter file, look at the .sct file that was automatically generated by the toolchain when you build with the Use Memory Layout from Target Dialog option checked.  And of course read the manual.