misc: vexpress: Fix sparse non static symbol warnings
Fixes the following sparse warnings:
drivers/misc/vexpress-syscfg.c:133:22: warning:
symbol 'vexpress_syscfg_regmap_config' was not declared. Should it be static?
drivers/misc/vexpress-syscfg.c:279:5: warning:
symbol 'vexpress_syscfg_probe' was not declared. Should it be static?