pwm: th1520: Fix missing Kconfig dependencies

pwm: th1520: Fix missing Kconfig dependencies

The driver fails to build on configurations lacking COMMON_CLK (missing
clk::Clk) or HAS_IOMEM (incomplete `pwm_chip` struct on UML).

Add dependencies on ARCH_THEAD and HAS_IOMEM, and add COMMON_CLK to
ensure correct compilation and platform targeting.

Reported-by: Markus Probst <markus.probst@gmail.com>
Closes: https://lore.kernel.org/all/a66b337528d700ae92d7940a04c59206e06a8495.camel@posteo.de/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512020957.PqnHfe7C-lkp@intel.com/
Fixes: e03724aac758 ("pwm: Add Rust driver for T-HEAD TH1520 SoC")
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Link: https://patch.msgid.link/20251209-fix_deps_pwm-v1-1-f7ed8bd1bd3d@samsung.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>