efi_loader: avoid duplicate weak invalidate_icache_all()

efi_loader: avoid duplicate weak invalidate_icache_all()

If multiple weak implementations of a weak function exist, it is unclear
which one the linker should chose. cmd/cache.c already defines a weak
invalidate_icache_all().

We don't need a call to invalidate_icache_all() on x86.
ARM, RISC-V, and Sandbox provide an implementation.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>