vexpress: Initialise the sysregs before setting up the clocks

Following arm64 commit bc3ee18a (arm64: init: Move of_clk_init to
time_init()), vexpress_osc_of_setup() is called via of_clk_init() long
before initcalls are issued. Initialising the vexpress oscillators
requires the vespress sysregs to be already initialised, so this patch
adds an explicit call to vexpress_sysreg_of_early_init() in vexpress
oscillator setup function.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Tested-by: Pawel Moll <pawel.moll@arm.com>
Acked-by: Pawel Moll <pawel.moll@arm.com>
Cc: Mike Turquette <mturquette@linaro.org>