xilinx: versal: Enable CONFIG_POSITION_INDEPENDENT

U-Boot expects to be linked to a specific hard-coded address and to
be loaded to and run from that address. CONFIG_POSITION_INDEPENDENT
config lifts that restriction & allowing the code to be loaded to
and executed from almost any address.

As we enabled CONFIG_POSITION_INDEPENDENT, CONFIG_INIT_SP_RELATIVE
is enabled by default, where it will set the early stack pointer at
runtime by adding an offset value to &_bss_start. The offset value
is taken from SYS_INIT_SP_BSS_OFFSET.

SYS_INIT_SP_BSS_OFFSET offset should be large enough so that the
early malloc region, global data (gd), and early stack should fit.
With commit d8fabcc424bd ("arm64: versal: Increase SYS_MALLOC_F_LEN")
SYS_MALLOC_F_LEN is increased from 32KB to 1MB, so we need to
accommodate this space with SYS_INIT_SP_BSS_OFFSET. Hence increasing
SYS_INIT_SP_BSS_OFFSET to 1.5MB.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Acked-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>