问题现象：使用烧写器对GPMC初始化后可正常boot，拔掉烧写器后不能正常启动。
AM335x的手册中描述，boot时内部ROM code未对所有的GPMC引脚进行配置，只配置A0-A11.
AM437x也存在同样的问题吗？
SYSBOOT[4:0]=00101b
GPMC地址总线使用的引脚
a[11:0] →gpmc_a[11:0]
a[19:12] →dss_data[15:8]
a[23:20] →mmc0_dat[0:3]
a24 →mmc0_clk
a25 →mmc0_cmd
d[15:0] →gpmc_ad[15:0]
AM335x手册中的描述
26.1.8.2.2 Pins Used
The list of device pins that are configured by the ROM in the case of NOR boot mode are as follows.
Please note that all the pins might not be driven at boot time. The decision as to which pins need to be
driven is done based on the type of NOR flash selected. The pins that are not listed below are not
configured by the ROM code and are left at power-on defaults. Specifically, external logic is needed to
isolate the upper address lines (A12–A27) of the NOR flash from the device pins and drive them low
during non-muxed NOR boot. Similarly for Muxed NOR Boot, address lines A16 and above to the memory
are not controlled by the ROM and need to be managed externally during boot to ensure proper
addressing to the all memory signals.
