ARM: dts: msm: Move boot_rom_ahb_clk to proxy voted for msm8998

Proxy vote for gcc_boot_rom_ahb_clk for modem pil on msm8998 instead
of keeping the vote until the modem was shutdown.

Change-Id: Ib32d40351179a687eca38228c4503e4a9a88c28d
Signed-off-by: Puja Gupta <pujag@codeaurora.org>