perf: xgene_pmu: Convert to devm_platform_ioremap_resource()

Use devm_platform_ioremap_resource() to simplify code.

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Link: https://lore.kernel.org/r/20230704093556.17926-1-frank.li@vivo.com
Signed-off-by: Will Deacon <will@kernel.org>