clk: Specify IOMEM dependency for HSDK pll driver

The HSDK pll driver uses the devm_ioremap_resource function, but does
not specify a dependency on IOMEM in Kconfig. This causes a build
failure on architectures without IOMEM, for example, UML (notably with
make allyesconfig).

Fix this by making CONFIG_CLK_HSDK depend on CONFIG_IOMEM.

Signed-off-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/r/20200630043214.1080961-1-davidgow@google.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>