Make bootrom depend on cluster configuration

[colluca]

The following address is hardcoded and breaks if the bootrom size, the scratch1 register offset or the number of instructions preceding these in the bootrom change. Generalize this.

snitch_cluster/target/snitch_cluster/test/bootrom.S

Lines 24 to 28 in 24463ca

	# This offset can be calculated as follows:
	# - 0x20 (start of this bootrom)
	# + 0x1000 (bootrom size 4kB)
	# + 0x188 (offset of the scratch1 register)
	li t1, 0x1168