lmb: Add generic arch_lmb_reserve_generic()

lmb: Add generic arch_lmb_reserve_generic()

The arc/arm/m68k/microblaze/mips/ppc arch_lmb_reserve() implementations
are all mostly the same, except for a couple of details. Implement a
generic arch_lmb_reserve_generic() function which can be parametrized
enough to cater for those differences between architectures. This can
also be parametrized enough so it can handle cases where U-Boot is not
relocated to the end of DRAM e.g. because there is some other reserved
memory past U-Boot (e.g. unmovable firmware for coprocessor), it is not
relocated at all, and other such use cases.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Alexey Brodkin <alexey.brodkin@synopsys.com>
Cc: Angelo Dureghello <angelo@sysam.it>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Cc: Hai Pham <hai.pham.ud@renesas.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Wolfgang Denk <wd@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>